EX-21

Exhibit 21

SUBSIDIARIES OF ADTRAN, INC.

December 31, 2016

Name of Subsidiary	Country or State of Incorporation
ADTRAN Networks Pty. Ltd	Australia
ADTRAN Networks Comunicações Ltda.	Brazil
ADTRAN Canada, Inc.	Canada
ADTRAN Networks Canada, Inc.	Canada
ADTRAN d.o.o.	Croatia
ADTRAN International, Inc.	Delaware
ADTRAN Networks Worldwide, Inc.	Delaware
ADTRAN Networks, LLC	Delaware
Bluesocket, Inc.	Delaware
ADTRAN Oy	Finland
ADTRAN GmbH	Germany
ADTRAN Networks M.E.P.E.	Greece
ADTRAN Networks Hong Kong Limited	Hong Kong
ADTRAN Networks India Private Limited	India
ADTRAN Holdings Ltd.	Israel
ADTRAN S.R.L.	Italy
ADTRAN K.K.	Japan
ADTRAN Networks Sdn Bhd	Malaysia
ADTRAN Networks S.A. de C.V.	Mexico
ADTRAN Networks & Services, S. de R.L. de C.V.	Mexico
ADTRAN Peru S.R.L.	Peru
ADTRAN Sp. z.o.o.	Poland
ADTRAN, Unipessoal Lda.	Portugal
ADTRAN LLC	Russia
ADTRAN International, Inc. - Saudi Arabia branch	Saudi Arabia
ADTRAN Singapore Pte. Ltd.	Singapore
ADTRAN s.r.o.	Slovakia
ADTRAN Proprietary Ltd.	South Africa
ADTRAN Switzerland GmbH	Switzerland
ADTRAN Europe Limited	United Kingdom

EX-23

Exhibit 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in the Registration Statements on Form S-8 (Nos. 333-215218, 333-168419, 333-133927, 333-126734, 333-66000, 333-41458, 333-78417, 333-30375, 333-29899, 333-4808) of ADTRAN, Inc. of our report dated February 24, 2017 relating to the financial statements, financial statement schedule and the effectiveness of internal control over financial reporting, which appears in this Form 10-K.

/s/ PricewaterhouseCoopers LLP

Birmingham, Alabama

February 24, 2017

EX-24

Exhibit 24

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned constitutes and appoints Thomas R. Stanton and Roger D. Shannon, and each of them, his true and lawful attorneys-in-fact and agents, with full power of substitution, for him and in his name, place and stead, in any and all capacities, to sign the Annual Report on Form 10-K of ADTRAN, Inc. for the fiscal year ended December 31, 2016 and any and all amendments thereto, and other documents in connection therewith and to file the same, with all exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission and the NASDAQ Global Select Market, Inc., granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done, as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

This 24^th day of February 2017

/s/ H. Fenwick Huss

H. Fenwick Huss

Director

/s/ William L. Marks

William L. Marks

Director

/s/ Anthony Melone

Anthony Melone

Director

/s/ Balan Nair

Balan Nair

Director

/s/ Jacqueline H. Rice

Jacqueline H. Rice

Director

/s/ Kathryn A. Walker

Kathryn A. Walker

Director

EX-31

Exhibit 31

CERTIFICATIONS

I, Thomas R. Stanton, certify that:

1. I have reviewed this Annual Report on Form 10-K of ADTRAN, Inc.;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s Board of Directors (or persons performing the equivalent functions):

(a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

(b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: February 24, 2017

/s/ Thomas R. Stanton

Thomas R. Stanton

Chief Executive Officer and Chairman of the Board

I, Roger D. Shannon, certify that:

1. I have reviewed this Annual Report on Form 10-K of ADTRAN, Inc.;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s Board of Directors (or persons performing the equivalent functions):

(a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

(b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: February 24, 2017

/s/ Roger D. Shannon

Roger D. Shannon

Senior Vice President of Finance,

Chief Financial Officer,

Corporate Secretary and Treasurer

EX-32

Exhibit 32

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report of ADTRAN, Inc. (the “Company”) on Form 10-K for the period ended December 31, 2016 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Thomas R. Stanton, Chief Executive Officer and Chairman of the Board of the Company, certify, pursuant to 18 U.S.C. § 1350, as adopted pursuant to § 906 of the Sarbanes-Oxley Act of 2002, that, to the best of my knowledge:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ Thomas R. Stanton

Thomas R. Stanton

Chief Executive Officer and Chairman of the Board

Date: February 24, 2017

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report of ADTRAN, Inc. (the “Company”) on Form 10-K for the period ended December 31, 2016 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Roger D. Shannon, Senior Vice President of Finance, Chief Financial Officer, Corporate Secretary and Treasurer of the Company, certify, pursuant to 18 U.S.C. § 1350, as adopted pursuant to § 906 of the Sarbanes-Oxley Act of 2002, that, to the best of my knowledge:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ Roger D. Shannon

Roger D. Shannon

Senior Vice President of Finance,

Chief Financial Officer,  

Corporate Secretary and Treasurer

Date: February 24, 2017

XML

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Feb. 09, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	FY
Trading Symbol	ADTN
Entity Registrant Name	ADTRAN INC
Entity Central Index Key	0000926282
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		48,519,654
Entity Public Float			$ 903,566,094

XML

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current Assets
Cash and cash equivalents	$ 79,895	$ 84,550
Short-term investments	43,188	34,396
Accounts receivable, less allowance for doubtful accounts of $— and $19 at December 31, 2016 and 2015, respectively	92,346	71,917
Other receivables	15,137	19,321
Income tax receivable, net	760
Inventory, net	105,117	91,533
Prepaid expenses and other current assets	16,459	10,145
Total Current Assets	352,902	311,862
Property, plant and equipment, net	84,469	73,233
Deferred tax assets, net	38,036	37,015
Goodwill	3,492	3,492
Other assets	12,234	9,276
Long-term investments	176,102	198,026
Total Assets	667,235	632,904
Current Liabilities
Accounts payable	77,342	48,668
Unearned revenue	16,326	16,615
Accrued expenses	12,434	12,108
Accrued wages and benefits	20,433	12,857
Income tax payable, net		2,395
Total Current Liabilities	126,535	92,643
Non-current unearned revenue	6,333	7,965
Other non-current liabilities	28,050	24,236
Bonds payable	26,800	27,900
Total Liabilities	187,718	152,744
Commitments and contingencies (see Note 13)
Stockholders' Equity
Common stock, par value $0.01 per share; 200,000 shares authorized; 79,652 shares issued and 48,472 shares outstanding at December 31, 2016 and 79,652 shares issued and 49,558 shares outstanding at December 31, 2015	797	797
Additional paid-in capital	252,957	246,879
Accumulated other comprehensive loss	(12,188)	(8,969)
Retained earnings	921,942	906,772
Less treasury stock at cost: 31,180 and 30,094 shares at December 31, 2016 and 2015, respectively	(683,991)	(665,319)
Total Stockholders' Equity	479,517	480,160
Total Liabilities and Stockholders' Equity	$ 667,235	$ 632,904

XML

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts		$ 19
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	79,652,000	79,652,000
Common stock, shares outstanding	48,472,000	49,558,000
Treasury stock, shares	31,180,000	30,094,000

XML

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Sales
Products	$ 525,502	$ 527,422	$ 559,532
Services	111,279	72,642	70,475
Total Sales	636,781	600,064	630,007
Cost of Sales
Products	270,695	293,843	288,015
Services	74,742	39,324	30,665
Total Cost of Sales	345,437	333,167	318,680
Gross Profit	291,344	266,897	311,327
Selling, general and administrative expenses	131,805	123,542	131,958
Research and development expenses	124,804	129,876	132,258
Operating Income	34,735	13,479	47,111
Interest and dividend income	3,918	3,953	5,019
Interest expense	(572)	(596)	(677)
Net realized investment gain	5,923	10,337	7,278
Other income (expense), net	(651)	(1,465)	1,175
Gain on bargain purchase of a business	3,542
Income before provision for income taxes	46,895	25,708	59,906
Provision for income taxes	(11,666)	(7,062)	(15,286)
Net Income	$ 35,229	$ 18,646	$ 44,620
Weighted average shares outstanding – basic	48,724	51,145	55,120
Weighted average shares outstanding – diluted	48,949	51,267	55,482
Earnings per common share – basic	$ 0.72	$ 0.36	$ 0.81
Earnings per common share – diluted	$ 0.72	$ 0.36	$ 0.80

XML

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 35,229	$ 18,646	$ 44,620
Other Comprehensive Loss, net of tax:
Net unrealized losses on available-for-sale securities	(1,528)	(7,032)	(1,773)
Defined benefit plan adjustments	(1,122)	1,862	(4,866)
Foreign currency translation	(569)	(3,724)	(4,189)
Other Comprehensive Loss, net of tax	(3,219)	(8,894)	(10,828)
Comprehensive Income, net of tax	$ 32,010	$ 9,752	$ 33,792

XML

Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income [Member]
Beginning Balance at Dec. 31, 2013	$ 604,606	$ 797	$ 233,511	$ 884,451	$ (524,906)	$ 10,753
Beginning Balance, Shares at Dec. 31, 2013		79,652
Net Income	44,620			44,620
Other comprehensive loss, net of tax	(10,828)					(10,828)
Dividend payments	(19,947)			(19,947)
Dividends accrued for unvested restricted stock units	(19)			(19)
Stock options exercised	2,839			(558)	3,397
PSUs and restricted stock vested	(326)		(326)	(796)	796
Purchase of treasury stock	(80,576)				(80,576)
Income tax effect of stock compensation arrangements	81		81
Stock-based compensation expense	8,563		8,563
Ending Balance at Dec. 31, 2014	549,013	$ 797	241,829	907,751	(601,289)	(75)
Ending Balance, Shares at Dec. 31, 2014		79,652
Net Income	18,646			18,646
Other comprehensive loss, net of tax	(8,894)					(8,894)
Dividend payments	(18,449)			(18,449)
Dividends accrued for unvested restricted stock units	(7)			(7)
Stock options exercised	961			(402)	1,363
PSUs and restricted stock vested	(69)		(69)	(767)	767
Purchase of treasury stock	(66,160)				(66,160)
Income tax effect of stock compensation arrangements	(1,593)		(1,593)
Stock-based compensation expense	6,712		6,712
Ending Balance at Dec. 31, 2015	$ 480,160	$ 797	246,879	906,772	(665,319)	(8,969)
Ending Balance, Shares at Dec. 31, 2015	79,652	79,652
Net Income	$ 35,229			35,229
Other comprehensive loss, net of tax	(3,219)					(3,219)
Dividend payments	(17,583)			(17,583)
Dividends accrued for unvested restricted stock units	(48)			(48)
Stock options exercised	4,717			(1,499)	6,216
PSUs and restricted stock vested	(142)		(142)	(929)	929
Purchase of treasury stock	(25,817)				(25,817)
Income tax effect of stock compensation arrangements	(475)		(475)
Stock-based compensation expense	6,695		6,695
Ending Balance at Dec. 31, 2016	$ 479,517	$ 797	$ 252,957	$ 921,942	$ (683,991)	$ (12,188)
Ending Balance, Shares at Dec. 31, 2016	79,652	79,652

XML

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock options exercised, shares	283	60	147
PSUs and restricted stock vested, shares	42	34	35
Treasury Stock [Member]
Purchase of treasury stock, shares	1,411	3,967	3,669

XML

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net income	$ 35,229	$ 18,646	$ 44,620
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,407	14,245	14,845
Amortization of net premium on available-for-sale investments	643	2,402	4,360
Net realized gain on long-term investments	(5,923)	(10,337)	(7,278)
Net loss on disposal of property, plant and equipment	22	644	142
Gain on bargain purchase of a business	(3,542)
Stock-based compensation expense	6,695	6,712	8,563
Deferred income taxes	(2,685)	(692)	(5,526)
Tax impact of stock option exercises		(40)	81
Excess tax benefits from stock-based compensation arrangements	(2)	(3)	(63)
Change in operating assets and liabilities:
Accounts receivable, net	(21,302)	14,918	(3,910)
Other receivables	4,101	11,704	(19,298)
Inventory	(10,887)	(6,877)	2,144
Prepaid expenses and other assets	(7,108)	(5,070)	(3,818)
Accounts payable	26,722	(5,826)	9,973
Accrued expenses and other liabilities	8,792	(10,289)	(166)
Income taxes payable, net	(3,162)	(11,590)	11,168
Net cash provided by operating activities	42,000	18,547	55,837
Cash flows from investing activities
Purchases of property, plant and equipment	(21,441)	(11,753)	(11,256)
Proceeds from disposals of property, plant and equipment		183	1
Proceeds from sales and maturities of available-for-sale investments	225,075	280,435	230,019
Purchases of available-for-sale investments	(209,172)	(188,921)	(142,695)
Acquisition of business	(943)
Net cash provided by (used in) investing activities	(6,481)	79,944	76,069
Cash flows from financing activities
Proceeds from stock option exercises	4,717	961	2,839
Purchases of treasury stock	(25,817)	(66,160)	(80,576)
Dividend payments	(17,583)	(18,449)	(19,947)
Payments on long-term debt	(1,100)	(1,100)	(16,500)
Excess tax benefits from stock-based compensation arrangements	2	3	63
Net cash used in financing activities	(39,781)	(84,745)	(114,121)
Net increase (decrease) in cash and cash equivalents	(4,262)	13,746	17,785
Effect of exchange rate changes	(393)	(2,635)	(2,644)
Cash and cash equivalents, beginning of year	84,550	73,439	58,298
Cash and cash equivalents, end of year	79,895	84,550	73,439
Supplemental disclosure of cash flow information
Cash paid during the year for interest	575	598	758
Cash paid during the year for income taxes	18,689	20,139	9,856
Supplemental disclosure of non-cash investing activities
Purchases of property, plant and equipment included in accounts payable	$ 2,103	$ 598	$ 467

XML

Nature of Business and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2016

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Nature of Business and Summary of Significant Accounting Policies

Note 1 – Nature of Business and Summary of Significant Accounting Policies

ADTRAN, Inc. is a leading global provider of networking and communications equipment. Our solutions enable voice, data, video and Internet communications across a variety of network infrastructures. These solutions are deployed by many of the United States’ and the world’s largest CSPs, distributed enterprises and small and medium-sized businesses, public and private enterprises, and millions of individual users worldwide.

Principles of Consolidation

Our consolidated financial statements include ADTRAN and its wholly owned subsidiaries. All inter-company accounts and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expense during the reporting period. Our more significant estimates include the obsolete and excess inventory reserves, warranty reserves, customer rebates, determination of the deferred revenue components of multiple element sales agreements, estimated costs to complete obligations associated with deferred revenues and network installations, estimated income tax provision and income tax contingencies, the fair value of stock- based compensation, impairment of goodwill, valuation and estimated lives of intangible assets, estimated pension liability, fair value of investments, and the evaluation of other-than-temporary declines in the value of investments. Actual amounts could differ significantly from these estimates.

Cash and Cash Equivalents

Cash and cash equivalents represent demand deposits, money market funds, and short-term investments classified as available-for-sale with original maturities of three months or less. We maintain depository investments with certain financial institutions. Although these depository investments may exceed government insured depository limits, we have evaluated the credit worthiness of these applicable financial institutions, and determined the risk of material financial loss due to the exposure of such credit risk to be minimal. As of December 31, 2016, $77.9 million of our cash and cash equivalents, primarily certain domestic money market funds and foreign depository accounts, were in excess of government provided insured depository limits.

Financial Instruments

The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents, accounts receivable, and accounts payable approximate fair value due to the immediate or short-term maturity of these financial instruments. The carrying amount reported for bonds payable was $27.8 million, compared to an estimated fair value of $28.1 million, based on a debt security with a comparable interest rate and maturity and a Standard & Poor’s credit rating of AAA.

Investments with contractual maturities beyond one year, such as our variable rate demand notes, may be classified as short-term based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. Despite the long-term nature of their stated contractual maturities, we routinely buy and sell these securities and we believe we have the ability to quickly sell them to the remarketing agent, tender agent, or issuer at par value plus accrued interest in the event we decide to liquidate our investment in a particular variable rate demand note. All income generated from these investments was recorded as interest income. We have not been required to record any losses relating to variable rate demand notes.

Long-term investments represent a restricted certificate of deposit held at cost, deferred compensation plan assets, corporate bonds, municipal fixed-rate bonds, asset-backed bonds, mortgage/agency backed bonds, U.S. and foreign government bonds, variable rate demand notes, marketable equity securities, and other equity investments. Marketable equity securities are reported at fair value as determined by the most recently traded price of the securities at the balance sheet date, although the securities may not be readily marketable due to the size of the available market. Unrealized gains and losses, net of tax, are reported as a separate component of stockholders’ equity. Realized gains and losses on sales of securities are computed under the specific identification method and are included in current income. We review our investment portfolio quarterly for investments considered to have sustained an other-than-temporary decline in value. Impairment charges for other-than-temporary declines in value are recorded as realized losses in the accompanying consolidated statements of income. All of our investments at December 31, 2016 and 2015 are classified as available-for-sale securities. See Note 4 of Notes to Consolidated Financial Statements for additional information.

Accounts Receivable

We record accounts receivable at net realizable value. Prior to establishing payment terms for a new customer, we evaluate the credit risk of the customer. Credit limits and payment terms established for new customers are re-evaluated periodically based on customer collection experience and other financial factors. At December 31, 2016, three customers accounted for 63.3% of our total accounts receivable. At December 31, 2015, three customers accounted for 37.3% of our total accounts receivable.

We maintain an allowance for doubtful accounts for losses resulting from the inability of our customers to make required payments. We regularly review the allowance for doubtful accounts and consider factors such as the age of accounts receivable balances, the current economic conditions that may affect a customer’s ability to pay, significant one-time events and our historical experience. If the financial condition of a customer deteriorates, resulting in an impairment of their ability to make payments, we may be required to record an allowance for doubtful accounts. If circumstances change with regard to individual receivable balances that have previously been determined to be uncollectible (and for which a specific reserve has been established), a reduction in our allowance for doubtful accounts may be required. Our allowance for doubtful accounts was nil and $19 thousand at December 31, 2016 and December 31, 2015, respectively.

Other Receivables

Other receivables are comprised primarily of amounts due from subcontract manufacturers for product component transfers, accrued interest on investments and on a restricted certificate of deposit, amounts due from various jurisdictions for value-added tax, and amounts due from employee stock option exercises.

Inventory

Inventory is carried at the lower of cost or market, with cost being determined using the first-in, first-out method. Standard costs for material, labor and manufacturing overhead are used to value inventory. Standard costs are updated at least quarterly; therefore, inventory costs approximate actual costs at the end of each reporting period. We establish reserves for estimated excess, obsolete or unmarketable inventory equal to the difference between the cost of the inventory and the estimated fair value of the inventory based upon assumptions about future demand, market conditions and age. When we dispose of excess and obsolete inventories, the related disposals are charged against the inventory reserve. See Note 6 of Notes to Consolidated Financial Statements for additional information.

Property, Plant and Equipment

Property, plant and equipment, which is stated at cost, is depreciated using the straight-line method over the estimated useful lives of the assets. We depreciate building and land improvements from five to 39 years, office machinery and equipment from three to seven years, engineering machinery and equipment from three to seven years, and computer software from three to five years. Expenditures for repairs and maintenance are charged to expense as incurred. Betterments that materially prolong the lives of the assets are capitalized. Gains and losses on the disposal of property, plant and equipment are recorded in operating income. See Note 7 of Notes to Consolidated Financial Statements for additional information.

Liability for Warranty

Our products generally include warranties of 90 days to five years for product defects. We accrue for warranty returns at the time revenue is recognized based on our estimate of the cost to repair or replace the defective products. We engage in extensive product quality programs and processes, including actively monitoring and evaluating the quality of our component suppliers. Our products continue to become more complex in both size and functionality as many of our product offerings migrate from line card applications to total systems. The increasing complexity of our products will cause warranty incidences, when they arise, to be more costly. Our estimates regarding future warranty obligations may change due to product failure rates, material usage, and other rework costs incurred in correcting a product failure. In addition, from time to time, specific warranty accruals may be recorded if unforeseen problems arise. Should our actual experience relative to these factors be worse than our estimates, we will be required to record additional warranty expense. Alternatively, if we provide for more reserves than we require, we will reverse a portion of such provisions in future periods. During 2016, we incurred an increase in warranty expense related to a product recall caused by a defect in a part provided by a third party supplier. The liability for warranty obligations totaled $8.5 million and $8.7 million at December 31, 2016 and 2015, respectively. These liabilities are included in accrued expenses in the accompanying consolidated balance sheets.

A summary of warranty expense and write-off activity for the years ended December 31, 2016, 2015 and 2014 is as follows:

Year Ended December 31,	2016			2015			2014
(In thousands)
Balance at beginning of period	$	8,739		$	8,415		$	8,977
Plus: Amounts charged to cost and expenses		8,561			2,998			3,103
Less: Deductions		(8,752	)		(2,674	)		(3,665	)
Balance at end of period	$	8,548		$	8,739		$	8,415

Pension Benefit Plan Obligations

We maintain a defined benefit pension plan covering employees in certain foreign countries. Pension benefit plan obligations are based on various assumptions used by our actuaries in calculating these amounts. These assumptions include discount rates, compensation rate increases, expected return on plan assets, retirement rates and mortality rates. Actual results that differ from the assumptions and changes in assumptions could affect future expenses and obligations.

Stock-Based Compensation

We have two Board and stockholder approved stock incentive plans from which stock options and other awards are available for grant to employees and directors. All employee and director stock options granted under our stock option plans have an exercise price equal to the fair market value of the award, as defined in the plan, of the underlying common stock on the grant date. There are currently no vesting provisions tied to performance or market conditions for any stock awards. Vesting for all outstanding award grants is based only on continued service as an employee or director of ADTRAN. All of our outstanding stock option awards are classified as equity awards.

Under the provisions of our approved plans, we made grants of performance stock units to certain of our executive officers in 2016, 2015, and 2014. The performance stock units are subject to a market condition based on the relative total shareholder return of ADTRAN against all the companies in the NASDAQ Telecommunications Index and vest at the end of a three-year performance period. The performance stock units are converted into shares of common stock upon vesting. Depending on the relative total shareholder return over the performance period, the executive officers may earn from 0% to 150% of the number of restricted stock units granted. The fair value of the award is based on the market price of our common stock on the date of grant, adjusted for the expected outcome of the impact of market conditions using a Monte Carlo Simulation valuation method. The recipients of the performance stock units also earn dividend credits during the performance period, which are paid in cash upon the issuance of common stock for the restricted stock units.

Stock-based compensation expense recognized in 2016, 2015 and 2014 was approximately $6.7 million, $6.7 million and $8.6 million, respectively. As of December 31, 2016, total compensation cost related to non-vested stock options, restricted stock units, performance stock units and restricted stock not yet recognized was approximately $16.4 million, which is expected to be recognized over an average remaining recognition period of 2.9 years. See Note 3 of Notes to Consolidated Financial Statements for additional information.

Impairment of Long-Lived Assets

We review long-lived assets used in operations for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable and the undiscounted cash flows estimated to be generated by the asset are less than the asset’s carrying value. An impairment loss would be recognized in the amount by which the recorded value of the asset exceeds the fair value of the asset, measured by the quoted market price of an asset or an estimate based on the best information available in the circumstances. There were no impairment losses recognized during 2016, 2015 or 2014.

Goodwill and Purchased Intangible Assets

We evaluate the carrying value of goodwill during the fourth quarter of each year and between annual evaluations if events occur or circumstances change that would more likely than not reduce the fair value of the reporting unit below its carrying amount. We have elected to first assess the qualitative factors to determine whether it is more likely than not that the fair value of the reporting unit to which the goodwill is assigned is less than its carrying amount as a basis for determining whether it is necessary to perform the two-step impairment test. If we determine that it is more likely than not that its fair value is less than its carrying amount, then the two-step impairment test will be performed. Based on the results of our qualitative assessment in 2016, we concluded that it was not necessary to perform the two-step impairment test. There have been no impairment losses recognized since the acquisition in 2011. Purchased intangible assets with finite lives are carried at cost, less accumulated amortization. Amortization is recorded over the estimated useful lives of the respective assets, which is 9 months to 14 years.

Research and Development Costs

Research and development costs include compensation for engineers and support personnel, outside contracted services, depreciation and material costs associated with new product development, the enhancement of current products, and product cost reductions. We continually evaluate new product opportunities and engage in intensive research and product development efforts. Research and development costs totaled $124.8 million, $129.9 million and $132.3 million for the years ended December 31, 2016, 2015 and 2014, respectively.

Other Comprehensive Income

Other comprehensive income consists of unrealized gains (losses) on available-for-sale securities, reclassification adjustments for amounts included in net income related to impairments of available-for-sale securities and realized gains (losses) on available-for-sale securities, defined benefit plan adjustments and foreign currency translation adjustments.

The following table presents changes in accumulated other comprehensive income, net of tax, by component for the years ended December 31, 2014, 2015 and 2016:

(In thousands)	Unrealized Gains (Losses) on Available- for-Sale Securities			Defined Benefit Plan Adjustments			Foreign Currency Adjustments			Total
Balance at December 31, 2013	$	10,737		$	(891	)	$	907		$	10,753
Other comprehensive income (loss) before    reclassifications		2,363			(4,866	)		(4,189	)		(6,692	)
Amounts reclassified from accumulated other    comprehensive income		(4,136	)		—			—			(4,136	)
Balance at December 31, 2014		8,964			(5,757	)		(3,282	)		(75	)
Other comprehensive income (loss) before    reclassifications		(844	)		1,589			(3,724	)		(2,979	)
Amounts reclassified from accumulated other    comprehensive income		(6,188	)		273			—			(5,915	)
Balance at December 31, 2015		1,932			(3,895	)		(7,006	)		(8,969	)
Other comprehensive income (loss) before    reclassifications		1,515			(1,229	)		(569	)		(283	)
Amounts reclassified from accumulated other    comprehensive income		(3,043	)		107			—			(2,936	)
Balance at December 31, 2016	$	404		$	(5,017	)	$	(7,575	)	$	(12,188	)

The following tables present the details of reclassifications out of accumulated other comprehensive income for the years ended December 31, 2016, 2015 and 2014:

(In thousands)	2016
Details about Accumulated Other Comprehensive Income Components	Amount Reclassified from Accumulated Other Comprehensive Income			Affected Line Item in the Statement Where Net Income Is Presented
Unrealized gains (losses) on available-for-sale securities:
Net realized gain on sales of securities	$	5,408		Net realized investment gain
Impairment expense		(419	)	Net realized investment gain
Defined benefit plan adjustments – actuarial losses		(156	)	(1)
Total reclassifications for the period, before tax		4,833
Tax (expense) benefit		(1,897	)
Total reclassifications for the period, net of tax	$	2,936

⁽¹⁾ Included in the computation of net periodic pension cost. See Note 11 of Notes to Consolidated Financial Statements.

(In thousands)	2015
Details about Accumulated Other Comprehensive Income Components	Amount Reclassified from Accumulated Other Comprehensive Income			Affected Line Item in the Statement Where Net Income Is Presented
Unrealized gains (losses) on available-for-sale securities:
Net realized gain on sales of securities	$	10,348		Net realized investment gain
Impairment expense		(203	)	Net realized investment gain
Defined benefit plan adjustments – actuarial losses		(396	)	(1)
Total reclassifications for the period, before tax		9,749
Tax (expense) benefit		(3,834	)
Total reclassifications for the period, net of tax	$	5,915

⁽¹⁾ Included in the computation of net periodic pension cost. See Note 11 of Notes to Consolidated Financial Statements.

(In thousands)	2014
Details about Accumulated Other Comprehensive Income Components	Amount Reclassified from Accumulated Other Comprehensive Income			Affected Line Item in the Statement Where Net Income Is Presented
Unrealized gains (losses) on available-for-sale securities:
Net realized gain on sales of securities	$	6,895		Net realized investment gain
Impairment expense		(115	)	Net realized investment gain
Total reclassifications for the period, before tax		6,780
Tax (expense) benefit		(2,644	)
Total reclassifications for the period, net of tax	$	4,136

The following tables present the tax effects related to the change in each component of other comprehensive income for the years ended December 31, 2016, 2015 and 2014:

	2016
(In thousands)	Before-Tax Amount			Tax (Expense) Benefit			Net-of-Tax Amount
Unrealized gains (losses) on available-for-sale securities	$	2,484		$	(969	)	$	1,515
Reclassification adjustment for amounts related to available-for-sale investments included in net income		(4,989	)		1,946			(3,043	)
Defined benefit plan adjustments		(1,782	)		553			(1,229	)
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income		156			(49	)		107
Foreign currency translation adjustment		(569	)		—			(569	)
Total Other Comprehensive Income (Loss)	$	(4,700	)	$	1,481		$	(3,219	)

	2015
(In thousands)	Before-Tax Amount			Tax (Expense) Benefit			Net-of-Tax Amount
Unrealized gains (losses) on available-for-sale securities	$	(1,384	)	$	540		$	(844	)
Reclassification adjustment for amounts related to available-    for-sale investments included in net income		(10,145	)		3,957			(6,188	)
Defined benefit plan adjustments		2,303			(714	)		1,589
Reclassification adjustment for amounts related to defined    benefit plan adjustments included in net income		396			(123	)		273
Foreign currency translation adjustment		(3,724	)		—			(3,724	)
Total Other Comprehensive Income (Loss)	$	(12,554	)	$	3,660		$	(8,894	)

	2014
(In thousands)	Before-Tax Amount			Tax (Expense) Benefit			Net-of-Tax Amount
Unrealized gains (losses) on available-for-sale securities	$	3,874		$	(1,511	)	$	2,363
Reclassification adjustment for amounts related to available-    for-sale investments included in net income		(6,780	)		2,644			(4,136	)
Defined benefit plan adjustments		(7,052	)		2,186			(4,866	)
Foreign currency translation adjustment		(4,189	)		—			(4,189	)
Total Other Comprehensive Income (Loss)	$	(14,147	)	$	3,319		$	(10,828	)

Income Taxes

The provision for income taxes has been determined using the asset and liability approach of accounting for income taxes. Under this approach, deferred taxes represent the future tax consequences expected to occur when the reported amounts of assets and liabilities are recovered or paid. The provision for income taxes represents income taxes paid or payable for the current year plus the change in deferred taxes during the year. Deferred taxes result from the difference between financial and tax bases of our assets and liabilities and are adjusted for changes in tax rates and tax laws when such changes are enacted. Valuation allowances are recorded to reduce deferred tax assets when it is more likely than not that a tax benefit will not be realized.

We establish reserves to remove some or all of the tax benefit of any of our tax positions at the time we determine that the positions become uncertain.  We adjust these reserves, including any impact on the related interest and penalties, as facts and circumstances change.

Foreign Currency

We record transactions denominated in foreign currencies on a monthly basis using exchange rates from throughout the year. Assets and liabilities denominated in foreign currencies are translated at the balance sheet dates using the closing rates of exchange between those foreign currencies and the functional currency with any transaction gains or losses reported in other income (expense). Our primary exposures to foreign currency exchange rate movements are with our German subsidiary, whose functional currency is the Euro, our Australian subsidiary, whose functional currency is the Australian dollar, and our Mexican subsidiary, whose functional currency is the U.S. dollar. Adjustments resulting from translating financial statements of international subsidiaries are recorded as a component of accumulated other comprehensive income (loss).

Revenue Recognition

Revenue is generally recognized when persuasive evidence of an arrangement exists, delivery has occurred, the product price is fixed or determinable, collection of the resulting receivable is reasonably assured, and product returns are reasonably estimable. For product sales, revenue is generally recognized upon shipment of the product to our customer in accordance with the title transfer terms of the sales agreement, generally Ex Works, per International Commercial Terms. In the case of consigned inventory, revenue is recognized when the end customer assumes ownership of the product. Contracts that contain multiple deliverables are evaluated to determine the units of accounting, and the consideration from the arrangement is allocated to each unit of accounting based on the relative selling price and corresponding terms of the contract. We use vendor-specific objective evidence of selling price. When this evidence is not available, we are generally not able to determine third-party evidence of selling price because of the extent of customization among competing products or services from other companies. In these instances, we use best estimates to allocate consideration to each respective unit of accounting. These estimates include analysis of respective bills of material and review and analysis of similar product and service offerings. We record revenue associated with installation services when respective contractual obligations are complete. In instances where customer acceptance is required, revenue is deferred until respective acceptance criteria have been met. Contracts that include both installation services and product sales are evaluated for revenue recognition in accordance with contract terms. As a result, installation services may be considered a separate deliverable or may be considered a combined single unit of accounting with the delivered product. Generally, either the purchaser, ADTRAN, or a third party can perform the installation of our products. Shipping fees are recorded as revenue and the related cost is included in cost of sales. Sales taxes invoiced to customers are included in revenues, and represent less than one percent of total revenues. The corresponding sales taxes paid are included in cost of goods sold. Value added taxes collected from customers in international jurisdictions are recorded in accrued expenses as a liability. Revenue is recorded net of discounts. Sales returns are recorded as a reduction of revenue and accrued based on historical sales return experience, which we believe provides a reasonable estimate of future returns.

A portion of our products are sold to a non-exclusive distribution network of major technology distributors in the United States. These large organizations then distribute or provide fulfillment services to an extensive network of VARs and SIs. VARs and SIs may be affiliated with us as a channel partner, or they may purchase from the distributor in an unaffiliated fashion. Additionally, with certain limitations our distributors may return unused and unopened product for stock-balancing purposes when such returns are accompanied by offsetting orders for products of equal or greater value.

We participate in cooperative advertising and market development programs with certain customers. We use these programs to reimburse customers for certain forms of advertising, and in general, to allow our customers credits up to a specified percentage of their net purchases. Our costs associated with these programs are estimated and included in marketing expenses in our consolidated statements of income. We also participate in rebate programs to provide sales incentives for certain products. Our costs associated with these programs are estimated and accrued at the time of sale, and are recorded as a reduction of sales in our consolidated statements of income.

Unearned Revenue

Unearned revenue primarily represents customer billings on our maintenance service programs and unearned revenues relating to multiple element contracts where we still have contractual obligations to our customers. We currently offer maintenance contracts ranging from one to five years. Revenue attributable to maintenance contracts is recognized on a straight-line basis over the related contract term. In addition, we provide software maintenance and a variety of hardware maintenance services to customers under contracts with terms up to ten years. When we defer revenue related to multiple-element contracts where we still have contractual obligations, we also defer the related costs. Deferred costs are included in prepaid expenses and other assets and totaled $10.7 million and $5.2 million at December 31, 2016 and 2015, respectively.

Other Income (Expense), Net

Other income (expense), net, is comprised primarily of miscellaneous income and expense, gains and losses on foreign currency transactions, and investment account management fees. For the year ended December 31, 2014, other income (expense), net included a $2.4 million gain related to the settlement of working capital items from an acquisition transaction that closed in 2012.

Earnings per Share

Earnings per common share, and earnings per common share assuming dilution, are based on the weighted average number of common shares and, when dilutive, common equivalent shares outstanding during the year. See Note 14 of Notes to Consolidated Financial Statements for additional information.

Dividends

During 2016, 2015 and 2014, we paid shareholder dividends totaling $17.6 million, $18.4 million and $19.9 million, respectively. The Board of Directors presently anticipates that it will declare a regular quarterly dividend so long as the present tax treatment of dividends exists and adequate levels of liquidity are maintained. The following table shows dividends paid to our shareholders in each quarter of 2016, 2015 and 2014.

Dividends per Common Share
	2016		2015		2014
First Quarter	$	0.09	$	0.09	$	0.09
Second Quarter	$	0.09	$	0.09	$	0.09
Third Quarter	$	0.09	$	0.09	$	0.09
Fourth Quarter	$	0.09	$	0.09	$	0.09

On January 17, 2017, the Board of Directors declared a quarterly cash dividend of $0.09 per common share to be paid to shareholders of record at the close of business on February 2, 2017. The ex-dividend date was January 31, 2017 and the payment date was February 16, 2017. The quarterly dividend payment was $4.4 million.

Business Combinations

We use the acquisition method to account for business combinations. Under the acquisition method of accounting, we recognize the assets acquired and liabilities assumed at their fair value on the acquisition date. Goodwill is measured as the excess of the consideration transferred over the net assets acquired. Costs incurred to complete the business combination, such as legal, accounting or other professional fees, are charged to general and administrative expenses as they are incurred.

Recently Issued Accounting Standards

In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) (ASU 2014-09), which supersedes the revenue recognition requirements in Topic 605, Revenue Recognition, including most industry-specific revenue recognition guidance throughout the Industry Topics of the Codification. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. In August 2015, the FASB issued ASU 2015-14, which deferred the effective date of ASU 2014-09 to fiscal years beginning after December 31, 2017, and interim periods within those fiscal years, with early adoption permitted for reporting periods beginning after December 15, 2016. Subsequently, the FASB issued ASUs in 2016 containing implementation guidance related to ASU 2014-09, including: ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net),which isintended to improve the operability and understandability of the implementation guidance on principal versus agent considerations; ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing,which is intended to clarify two aspects of Topic 606: identifying performance obligations and the licensing implementation guidance; ASU 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients,which contains certain provisions and practical expedients in response to identified implementation issues; and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, which is intended to clarify the Codification or to correct unintended application of guidance. ASU 2014-09 allows for either full retrospective or modified retrospective adoption. We plan to adopt ASU 2014-09 and the related ASUs on January 1, 2018, and we are currently evaluating the transition method that will be elected. We are continuing to evaluate the potential impact of these ASUs, and we believe the most significant potential impact relates to our accounting for software license and installation services revenues. We do not believe there will be a significant impact to product or maintenance revenues.

In July 2015, the FASB issued Accounting Standards Update No.  2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory (ASU 2015-11). Currently, Topic 330, Inventory, requires an entity to measure inventory at the lower of cost or market. Market could be replacement cost, net realizable value, or net realizable value less an approximately normal profit margin. ASU 2015-11 does not apply to inventory that is measured using last-in, first-out (LIFO) or the retail inventory method. The amendments apply to all other inventory, which includes inventory that is measured using first-in, first-out (FIFO) or average cost. ASU 2015-11 requires an entity to measure in scope inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. ASU 2015-11 is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. The amendments should be applied prospectively with earlier application permitted as of the beginning of an interim or annual reporting period. We adopted ASU 2015-05 in the first quarter of 2017, and there was no material impact on our financial position, results of operations and cash flows.

In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 requires an entity to recognize lease assets and lease liabilities on the balance sheet and to disclose key information about the entity's leasing arrangements. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. A modified retrospective approach is required. We anticipate the adoption of ASU 2016-02 will have a material impact on our financial position; however, we do not believe adoption will have a material impact on our results of operations. We believe the most significant impact relates to our accounting for operating leases for office space and equipment.

In March 2016, the FASB issued Accounting Standards Update No. 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting (ASU 2016-09). ASU 2016-09 simplifies several aspects of accounting for share-based compensation arrangements, including income tax effects, the classification of tax-related cash flows on the statement of cash flows, and accounting for forfeitures. ASU 2016-09 is effective for fiscal years beginning after December 15, 2016, including interim periods within those years. We adopted ASU 2016-09 in the first quarter of 2017, and there was no material impact on our financial position, results of operations and cash flows.

In January 2017, the FASB issued Accounting Standards Update No. 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04). ASU 2017-04 simplifies the measurement of goodwill by eliminating step 2 of the goodwill impairment test. Under ASU 2017-04, entities will be required to compare the fair value of a reporting unit to its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. ASU 2017-04 is effective for annual or interim impairment tests performed in fiscal years beginning after December 15, 2019, with early adoption permitted for annual or interim impairment tests performed on testing dates after January 1, 2017. The amendments should be applied prospectively. We do not expect the adoption of ASU 2017-04 will have a material impact on our financial position, results of operations or cash flows.

During 2016, we adopted the following accounting standards, which had no material effect on our financial position, results of operations or cash flows:

In April 2015, the FASB issued Accounting Standards Update No. 2015-05, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement (ASU 2015-05), which provides guidance on accounting for fees paid by a customer in a cloud computing arrangement. If a cloud computing arrangement includes a software license, then the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. ASU 2015-05 is effective for annual reporting periods beginning after December 15, 2015, including interim periods within that reporting period. The amendments may be applied either prospectively to all arrangements entered into or materially modified after the effective date or retrospectively. We adopted ASU 2015-05 during the first quarter of 2016 and will apply the new standard prospectively. The adoption of ASU 2015-05 did not have a material impact on our financial position, results of operations and cash flows.

In November 2015, the FASB issued Accounting Standards Update No. 2015-17, Balance Sheet Classification of Deferred Taxes (ASU 2015-17). ASU 2015-17 amends the existing guidance on income taxes to require the classification of all deferred tax assets and liabilities as non-current on the balance sheet. ASU 2015-17 is effective for fiscal years beginning after December 15, 2016, including interim periods within those years. Early adoption is permitted. The guidance may be applied either prospectively, for all deferred tax assets and liabilities, or retrospectively to all periods presented. We elected to early adopt ASU 2015-17 during the fourth quarter of 2016, and we applied the guidance retrospectively to all periods presented. As a result, $17.3 million and $18.9 million were reclassified from current deferred tax assets to non-current deferred tax assets at December 31, 2016 and 2015, respectively.

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Business Combinations

12 Months Ended

Dec. 31, 2016

Business Combinations [Abstract]

Business Combinations

Note 2 – Business Combinations

On September 13, 2016, we acquired key fiber access products, technologies and service relationships from subsidiaries of CommScope, Inc. for $0.9 million in cash. This acquisition will enhance our solutions for the cable MSO industry and will provide cable operators with the scalable solutions, services and support they require to compete in the multi-gigabit service delivery market. This transaction was accounted for as a business combination. We have included the financial results of this acquisition in our consolidated financial statements since the date of acquisition. These revenues are included in the Network Solutions reportable segment, and in the Access & Aggregation and Customer Devices categories.

We recorded a bargain purchase gain of $3.5 million, net of income taxes, subject to customary working capital adjustments between the parties. The bargain purchase gain represents the excess fair value of the net assets acquired over the consideration exchanged. We have assessed the recognition and measurement of the assets acquired and liabilities assumed based on historical and pro forma data for future periods and have concluded that our valuation procedures and resulting measures were appropriate. The gain is included in the line item “Gain on bargain purchase of a business” in the 2016 Consolidated Statements of Income.

The allocation of the purchase price to the estimated fair value of the assets acquired and liabilities assumed at the acquisition date, subject to working capital adjustments, is as follows:

(In Thousands)
Assets
Inventory	$	3,131
Property, plant and equipment		352
Intangible assets		4,700
Total assets acquired		8,183
Liabilities
Accounts payable		(1,250	)
Warranty payable		(61	)
Accrued wages and benefits		(122	)
Deferred income taxes		(2,265	)
Total liabilities assumed		(3,698	)
Total net assets		4,485
Gain on bargain purchase of a business, net of tax		(3,542	)
Total purchase price	$	943

The details of the acquired intangible assets are as follows:

In thousands	Value		Life (years)
Supply agreement	$	1,400		0.8
Customer relationships		1,200		6.0
Developed technology		800		10.0
License		500		1.3
Patent		500		7.3
Non-compete		200		2.3
Trade name		100		2.0
Total	$	4,700

The actual revenue and net loss included in our Consolidated Statements of Income for the period September 13, 2016 to December 31, 2016 are as follows:

(In thousands)	September 13 to December 31, 2016
Revenue	$	2,768
Net loss	$	(805	)

The following supplemental unaudited pro forma information presents the financial results as if the acquisition had occurred on January 1, 2015. This supplemental unaudited pro forma information does not purport to be indicative of what would have occurred had the acquisition been completed on January 1, 2015, nor is it indicative of any future results. Aside from revising the 2015 net income for the effect of the bargain purchase gain, there were no material, non-recurring adjustments to this unaudited pro forma information.

(In thousands)	2016		2015
Pro forma revenue	$	641,170	$	603,923
Pro forma net income	$	31,212	$	22,945

For the year ended December 31, 2016, we incurred acquisition and integration related expenses and amortization of acquired intangibles of $1.0 million related to this acquisition.

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Stock-Based Compensation

12 Months Ended

Dec. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 3 – Stock-Based Compensation

Stock Incentive Program Descriptions

On January 23, 2006, the Board of Directors adopted the ADTRAN, Inc. 2006 Employee Stock Incentive Plan (2006 Plan), which authorized 13.0 million shares of common stock for issuance to certain employees and officers through incentive stock options and non-qualified stock options, stock appreciation rights, restricted stock and restricted stock units (RSUs). The 2006 Plan was adopted by stockholder approval at our annual meeting of stockholders held on May 9, 2006. Options granted under the 2006 Plan typically become exercisable beginning after one year of continued employment, normally pursuant to a four-year vesting schedule beginning on the first anniversary of the grant date, and have a ten-year contractual term. The 2006 Plan was replaced on May 13, 2015 by the ADTRAN, Inc. 2015 Employee Stock Incentive Plan (2015 Plan). Expiration dates of options outstanding at December 31, 2016 under the 2006 Plan range from 2017 to 2024.

Our stockholders approved the 2010 Directors Stock Plan (2010 Directors Plan) on May 5, 2010, under which 0.5 million shares of common stock have been reserved. This plan replaces the 2005 Directors Stock Option Plan. Under the 2010 Directors Plan, the Company may issue stock options, restricted stock and RSUs to our non-employee directors. Stock awards issued under the 2010 Directors Plan normally become vested in full on the first anniversary of the grant date. Options issued under the 2010 Directors Plan have a ten-year contractual term. Expiration dates of options outstanding at December 31, 2016 under the 2010 Directors Plan range from 2017 to 2019.

On January 20, 2015, the Board of Directors adopted the ADTRAN, Inc. 2015 Employee Stock Incentive Plan (2015 Plan), which authorizes 7.7 million shares of common stock for issuance to certain employees and officers through incentive stock options and non-qualified stock options, stock appreciation rights, performance stock units (PSUs), restricted stock and RSUs. The 2015 Plan was adopted by stockholder approval at our annual meeting of stockholders held on May 13, 2015. PSUs, restricted stock and RSUs granted under the 2015 Plan reduce the shares authorized for issuance under the 2015 Plan by 2.5 shares of common stock for each share underlying the award. Options granted under the 2015 Plan typically become exercisable beginning after one year of continued employment, normally pursuant to a four-year vesting schedule beginning on the first anniversary of the grant date, and have a ten-year contractual term. Expiration dates of options outstanding at December 31, 2015 under the 2015 Plan range from 2025 to 2026.

The following table summarizes stock-based compensation expense related to stock options, PSUs, restricted stock and RSUs for the years ended December 31, 2016, 2015 and 2014, which was recognized as follows:

(In thousands)	2016			2015			2014
Stock-based compensation expense included in cost of    sales	$	389		$	280		$	479
Selling, general and administrative expense		3,341			3,261			4,185
Research and development expense		2,965			3,171			3,899
Stock-based compensation expense included in operating    expenses		6,306			6,432			8,084
Total stock-based compensation expense		6,695			6,712			8,563
Tax benefit for expense associated with non-qualified    options		(963	)		(862	)		(1,157	)
Total stock-based compensation expense, net of tax	$	5,732		$	5,850		$	7,406

Stock-based compensation expense recognized in our Consolidated Statements of Income for the years ended December 31, 2016, 2015 and 2014 is based on stock options, PSUs, restricted stock and RSUs ultimately expected to vest, and has been reduced for estimated forfeitures. Estimates for forfeiture rates are based upon historical experience and are evaluated quarterly. We expect our forfeiture rate for stock options and RSUs to be approximately 3.7% annually. We estimated a 0% forfeiture rate for our PSUs and restricted stock due to the limited number of recipients and historical experience for these awards.

Stock Options

The following table is a summary of our stock options outstanding as of December 31, 2015 and 2016 and the changes that occurred during 2016:

(In thousands, except per share amounts)	Number of Options			Weighted Average Exercise Price		Weighted Avg. Remaining Contractual Life in Years		Aggregate Intrinsic Value
Options outstanding, December 31, 2015		7,108		$	21.97		6.42	$	3,284
Options granted		19		$	18.24
Options exercised		(283	)	$	16.66
Options forfeited		(93	)	$	17.90
Options expired		(413	)	$	23.96
Options outstanding, December 31, 2016		6,338		$	22.14		5.63	$	16,972
Options vested and expected to vest, December 31, 2016		6,276		$	22.20		5.60	$	16,606
Options exercisable, December 31, 2016		4,757		$	23.67		4.73	$	9,137

At December 31, 2016, total compensation cost related to non-vested stock options not yet recognized was approximately $7.5 million, which is expected to be recognized over an average remaining recognition period of 2.1 years.

All of the options above were issued at exercise prices that approximated fair market value at the date of grant. At December 31, 2016, 5.6 million options were available for grant under the shareholder approved plans.

The aggregate intrinsic values in the table above represent the total pre-tax intrinsic value (the difference between ADTRAN’s closing stock price on the last trading day of 2016 and the exercise price, multiplied by the number of in-the-money options) that would have been received by the option holders had all option holders exercised their options on December 31, 2016. The amount of aggregate intrinsic value will change based on the fair market value of ADTRAN’s stock.

The total pre-tax intrinsic value of options exercised during 2016, 2015 and 2014 was $1.1 million, $0.1 million and $0.7 million, respectively. The fair value of options fully vesting during 2016, 2015 and 2014 was $5.7 million, $6.6 million and $7.7 million, respectively.

The following table further describes our stock options outstanding as of December 31, 2016:

	Options Outstanding						Options Exercisable
Range of Exercise Prices	Options Outstanding at 12/31/16 (In thousands)		Weighted Avg. Remaining Contractual Life in Years		Weighted Average Exercise Price		Options Exercisable at 12/31/16 (In thousands)		Weighted Average Exercise Price
$14.88 – 18.96		2,101		6.78	$	15.82		1,217	$	16.14
$18.97 – 23.45		1,380		5.79	$	20.17		881	$	20.84
$23.46 – 30.35		1,491		5.08	$	23.89		1,293	$	23.92
$30.36 – 41.92		1,366		4.29	$	31.94		1,366	$	31.94
		6,338						4,757

PSUs, restricted stock and RSUs

Under the 2015 Plan, awards other than stock options, including PSUs, restricted stock and RSUs, may be granted to certain employees and officers. Under our PSU program, the number of shares of common stock earned by a recipient pursuant to the PSUs is subject to a market condition based on ADTRAN’s relative total shareholder return against all companies in the NASDAQ Telecommunications Index at the end of a three-year performance period. Depending on the relative total shareholder return over the performance period, the recipient may earn from 0% to 150% of the shares underlying the PSUs, with the shares earned distributed upon the vesting of the PSUs at the end of the three-year performance period. The fair value of the award is based on the market price of our common stock on the date of grant, adjusted for the expected outcome of the impact of market conditions using a Monte Carlo Simulation valuation method. A portion of the granted PSUs also vest and the underlying shares become deliverable upon the death or disability of the recipient or upon a change of control of ADTRAN, as defined by the 2015 Plan. The recipients of the PSUs receive dividend credits based on the shares of common stock underlying the PSUs. The dividend credits are vested and earned in the same manner as the PSUs and are paid in cash upon the issuance of common stock for the PSUs. The fair value of restricted stock and RSUs is equal to the closing price of our stock on the business day immediately preceding the grant date. Restricted stock and RSUs vest ratably over one year and four year periods, respectively.

The following table is a summary of our PSUs, restricted stock and RSUs outstanding as of December 31, 2015 and 2016 and the changes that occurred during 2016:

(In thousands, except per share amounts)	Number of shares			Weighted Average Grant Date Fair Value
Unvested PSUs, restricted stock and RSUs outstanding,    December 31, 2015		106		$	21.09
PSUs, restricted stock and RSUs granted		460		$	20.63
PSUs, restricted stock and RSUs vested		(46	)	$	22.50
PSUs, restricted stock and RSUs forfeited		(1	)	$	20.00
Unvested RSUs and restricted stock outstanding,    December 31, 2016		519		$	20.51

At December 31, 2016, total compensation cost related to the non-vested portion of PSUs, restricted stock and RSUs not yet recognized was approximately $8.9 million, which is expected to be recognized over an average remaining recognition period of 3.6 years.

Valuation and Expense Information

We use the Black-Scholes option pricing model (Black-Scholes Model) for the purpose of determining the estimated fair value of stock option awards on the date of grant. The Black-Scholes Model requires the input of certain assumptions that involve judgment. Because our stock options have characteristics significantly different from those of traded options, and because changes in the input assumptions can materially affect the fair value estimate, existing models may not provide reliable measures of fair value of our stock options. We use a Monte Carlo Simulation valuation method to value our performance-based PSUs. The fair value of RSUs and restricted stock issued is equal to the closing price of our stock on the date of grant. We will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. If circumstances change, and additional data becomes available over time, we may change our assumptions and methodologies, which may materially impact our fair value determination.

The stock option pricing model requires the use of several assumptions that impact the fair value estimate. These variables include, but are not limited to, the volatility of our stock price and employee exercise behaviors. There were no changes made during 2016 to the methodology used to determine our assumptions.

The weighted-average estimated fair value of stock options granted to employees during the years ended December 31, 2016, 2015 and 2014 was $5.22 per share, $4.28 per share and $6.31 per share, respectively, with the following weighted-average assumptions:

	2016			2015			2014
Expected volatility		34.79	%		34.57	%		39.05	%
Risk-free interest rate		1.36	%		1.81	%		1.79	%
Expected dividend yield		1.98	%		2.35	%		1.90	%
Expected life (in years)		6.25			6.23			6.33

We based our estimate of expected volatility for the years ended December 31, 2016, 2015 and 2014 on the sequential historical daily trading data of our common stock for a period equal to the expected life of the options granted. The selection of the historical volatility method was based on available data indicating our historical volatility is as equally representative of our future stock price trends as is our implied volatility. We have no reason to believe the future volatility of our stock price is likely to differ from its past volatility. The risk-free interest rate assumption is based upon implied yields of U.S. Treasury zero-coupon bonds on the date of grant having a remaining term equal to the expected life of the options granted. The dividend yield is based on our historical and expected dividend payouts. The expected life of our stock options is based upon historical exercise and forfeiture activity of our previous stock-based grants with a ten-year contractual term.

The PSU pricing model also requires the use of several significant assumptions that impact the fair value estimate. The estimated fair value of the PSUs granted to employees during the years ended December 31, 2016, 2015 and 2014 was $23.50 per share, $17.64 per share and $22.11 per share, respectively, with the following assumptions:

	2016			2015			2014
Expected volatility		29.79	%		31.34	%		36.40	%
Risk-free interest rate		1.17	%		1.20	%		0.96	%
Expected dividend yield		1.80	%		2.35	%		1.89	%

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Investments

12 Months Ended

Dec. 31, 2016

Investments Debt And Equity Securities [Abstract]

Investments

Note 4 – Investments

At December 31, 2016, we held the following securities and investments, recorded at either fair value or cost:

								Fair Value /
	Amortized		Gross Unrealized					Carrying
(In thousands)	Cost		Gains		Losses			Value
Deferred compensation plan assets	$	12,367	$	2,271	$	(42	)	$	14,596
Corporate bonds		66,522		64		(174	)		66,412
Municipal fixed-rate bonds		11,799		12		(37	)		11,774
Asset-backed bonds		10,201		19		(14	)		10,206
Mortgage/Agency-backed bonds		13,080		15		(91	)		13,004
U.S. government bonds		30,022		15		(270	)		29,767
Foreign government bonds		3,729		2		(1	)		3,730
Variable rate demand notes		11,855		—		—			11,855
Marketable equity securities		30,571		311		(1,503	)		29,379
Available-for-sale securities held at fair value	$	190,146	$	2,709	$	(2,132	)	$	190,723
Restricted investment held at cost									27,800
Other investments									767
Total carrying value of available-for-sale investments								$	219,290

At December 31, 2015, we held the following securities and investments, recorded at either fair value or cost:

								Fair Value /
	Amortized		Gross Unrealized					Carrying
(In thousands)	Cost		Gains		Losses			Value
Deferred compensation plan assets	$	11,325	$	1,575	$	(66	)	$	12,834
Corporate bonds		58,328		20		(734	)		57,614
Municipal fixed-rate bonds		26,414		28		(18	)		26,424
Asset-backed bonds		19,281		2		(44	)		19,239
Mortgage/Agency-backed bonds		15,463		1		(91	)		15,373
Government bonds		35,646		—		(248	)		35,398
Marketable equity securities		31,643		4,301		(1,693	)		34,251
Available-for-sale securities held at fair value	$	198,100	$	5,927	$	(2,894	)	$	201,133
Restricted investment held at cost									30,000
Other investments held at cost									1,289
Total carrying value of available-for-sale investments								$	232,422

As of December 31, 2016, corporate bonds, municipal fixed-rate bonds, asset-backed bonds, mortgage/agency-backed bonds, U.S. government bonds, and foreign government bonds had the following contractual maturities:

(In thousands)	Corporate bonds		Municipal fixed-rate bonds		Asset-backed bonds		Mortgage / Agency-backed bonds		U.S. government bonds		Foreign government bonds
Less than one year	$	18,912	$	8,321	$	—	$	—	$	1,701	$	2,400
One to two years		32,497		1,703		635		976		4,903		1,330
Two to three years		11,486		351		2,415		980		13,072		—
Three to five years		3,517		1,399		5,402		—		10,091		—
Five to ten years		—		—		1,600		2,060		—		—
More than ten years		—		—		154		8,988		—		—
Total	$	66,412	$	11,774	$	10,206	$	13,004	$	29,767	$	3,730

Our investment policy provides limitations for issuer concentration, which limits, at the time of purchase, the concentration in any one issuer to 5% of the market value of our total investment portfolio.

We review our investment portfolio for potential “other-than-temporary” declines in value on an individual investment basis. We assess, on a quarterly basis, significant declines in value which may be considered other-than-temporary and, if necessary, recognize and record the appropriate charge to write-down the carrying value of such investments. In making this assessment, we take into consideration qualitative and quantitative information, including but not limited to the following: the magnitude and duration of historical declines in market prices, credit rating activity, assessments of liquidity, public filings, and statements made by the issuer. We generally begin our identification of potential other-than-temporary impairments by reviewing any security with a fair value that has declined from its original or adjusted cost basis by 25% or more for six or more consecutive months. We then evaluate the individual security based on the previously identified factors to determine the amount of the write-down, if any. For each of the years ended December 31, 2016, 2015 and 2014, we recorded a charge of $0.8 million, $0.2 million and $0.1 million, respectively, related to the other-than-temporary impairment of certain marketable equity securities and our deferred compensation plan assets.

Realized gains and losses on sales of securities are computed under the specific identification method. The following table presents gross realized gains and losses related to our investments for the years ended December 31, 2016, 2015 and 2014:

Year Ended December 31, (In thousands)	2016			2015			2014
Gross realized gains	$	7,530		$	10,906		$	7,586
Gross realized losses	$	(1,607	)	$	(569	)	$	(308	)

The following table presents the breakdown of investments with unrealized losses at December 31, 2016:

(In thousands)	Continuous Unrealized Loss Position for Less than 12 Months					Continuous Unrealized Loss Position for 12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Deferred compensation plan assets	$	294	$	(12	)	$	245	$	(30	)	$	539	$	(42	)
Corporate bonds		32,562		(166	)		2,722		(8	)		35,284		(174	)
Municipal fixed-rate bonds		8,936		(37	)		—		—			8,936		(37	)
Asset-backed bonds		2,986		(14	)		—		—			2,986		(14	)
Mortgage/Agency-backed bonds		7,842		(81	)		1,239		(10	)		9,081		(91	)
U.S. government bonds		26,449		(270	)		—		—			26,449		(270	)
Foreign government bonds		924		(1	)		—		—			924		(1	)
Marketable equity securities		21,607		(1,200	)		1,495		(303	)		23,102		(1,503	)
Total	$	101,600	$	(1,781	)	$	5,701	$	(351	)	$	107,301	$	(2,132	)

The following table presents the breakdown of investments with unrealized losses at December 31, 2015:

(In thousands)	Continuous Unrealized Loss Position for Less than 12 Months					Continuous Unrealized Loss Position for 12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Deferred compensation plan assets	$	1,243	$	(53	)	$	92	$	(13	)	$	1,335	$	(66	)
Corporate bonds		35,952		(566	)		3,042		(168	)		38,994		(734	)
Municipal fixed-rate bonds		9,160		(18	)		—		—			9,160		(18	)
Asset-backed bonds		16,857		(44	)		—		—			16,857		(44	)
Mortgage/Agency-backed bonds		15,216		(91	)		—		—			15,216		(91	)
Government bonds		35,397		(248	)		—		—			35,397		(248	)
Marketable equity securities		14,364		(1,564	)		374		(129	)		14,738		(1,693	)
Total	$	128,189	$	(2,584	)	$	3,508	$	(310	)	$	131,697	$	(2,894	)

The decrease in unrealized losses during 2016, as reflected in the table above, results from changes in market positions associated with our fixed income and equity investment portfolio. At December 31, 2016, a total of 293 of our marketable equity securities were in an unrealized loss position.

We have categorized our cash equivalents and our investments held at fair value into a three-level fair value hierarchy based on the priority of the inputs to the valuation technique for the cash equivalents and investments as follows: Level 1 - Values based on unadjusted quoted prices for identical assets or liabilities in an active market; Level 2 - Values based on quoted prices in markets that are not active or model inputs that are observable either directly or indirectly; Level 3 - Values based on prices or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs could include information supplied by investees.

	Fair Value Measurements at December 31, 2016 Using
(In thousands)	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	6,878	$	6,878	$	—	$	—
Commercial paper		17,222		—		17,222		—
Cash equivalents		24,100		6,878		17,222		—
Available-for-sale securities
Deferred compensation plan assets		14,596		14,596		—		—
Available-for-sale debt securities
Corporate bonds		66,412		—		66,412		—
Municipal fixed-rate bonds		11,774		—		11,774		—
Asset-backed bonds		10,206		—		10,206		—
Mortgage/Agency-backed bonds		13,004		—		13,004		—
U.S. government bonds		29,767		29,767		—		—
Foreign government bonds		3,730		—		3,730		—
Variable rate demand notes		11,855		—		11,855		—
Available-for-sale marketable equity securities
Marketable equity securities – technology industry		3,374		3,374		—		—
Marketable equity securities – other		26,005		26,005		—		—
Available-for-sale securities		190,723		73,742		116,981		—
Total	$	214,823	$	80,620	$	134,203	$	—
	Fair Value Measurements at December 31, 2015 Using
(In thousands)	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	1,271	$	1,271	$	—	$	—
Commercial paper		11,696		—		11,696		—
Cash equivalents		12,967		1,271		11,696		—
Available-for-sale securities
Deferred compensation plan assets		12,834		12,834		—		—
Available-for-sale debt securities
Corporate bonds		57,614		—		57,614		—
Municipal fixed-rate bonds		26,424		—		26,424		—
Asset-backed bonds		19,239		—		19,239		—
Mortgage/Agency-backed bonds		15,373		—		15,373		—
Government bonds		35,398		35,398		—		—
Available-for-sale marketable equity securities
Marketable equity securities – technology industry		5,384		5,384		—		—
Marketable equity securities – other		28,867		28,867		—		—
Available-for-sale securities		201,133		82,483		118,650		—
Total	$	214,100	$	83,754	$	130,346	$	—

The fair value of our Level 2 securities is calculated using a weighted average market price for each security. Market prices are obtained from a variety of industry standard data providers, security master files from large financial institutions, and other third-party sources. These multiple market prices are used as inputs into a distribution-curve-based algorithm to determine the daily market value of each security.

Our municipal variable rate demand notes have a structure that implies a standard expected market price. The frequent interest rate resets make it reasonable to expect the price to stay at par. These securities are priced at the expected market price.

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Derivative Instruments and Hedging Activities

12 Months Ended

Dec. 31, 2016

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Derivative Instruments and Hedging Activities

Note 5 – Derivative Instruments and Hedging Activities

We have certain customers and suppliers who are invoiced or pay in a non-functional currency. Changes in the monetary exchange rates may adversely affect our results of operations and financial condition, as these are remeasured to the functional currency through profit and loss. When appropriate, we enter into various derivative transactions to enhance our ability to manage the volatility relating to these typical business exposures. We do not hold or issue derivative instruments for trading or other speculative purposes. Our derivative instruments are recorded in the Consolidated Balance Sheets at their fair values. Our derivative instruments do not qualify for hedge accounting, and accordingly, all changes in the fair value of the instruments are recognized as other income (expense) in the Consolidated Statements of Income. Our derivative instruments are not subject to master netting arrangements and are not offset in the Consolidated Balance Sheets.

As of December 31, 2016, we had forward contracts outstanding with notional amounts totaling €5.5 million ($5.8 million), which mature in the first quarter of in 2017.

The fair values of our derivative instruments recorded in the Consolidated Balance Sheet as of December 31, 2016 and 2015 were as follows:

(In thousands)	Balance Sheet Location	2016		2015
Derivatives Not Designated as Hedging Instruments (Level 2):
Foreign exchange contracts – asset derivatives	Other receivables	$	159	$	—

The change in the fair values of our derivative instruments recorded in the Consolidated Statements of Income during the years ended December 31, 2016, 2015 and 2014 were as follows:

(In thousands)	Income Statement Location	2016		2015		2014
Derivatives Not Designated as Hedging Instruments:
Foreign exchange contracts	Other income (expense)	$	724	$	511	$	1,852

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Inventory

12 Months Ended

Dec. 31, 2016

Inventory Disclosure [Abstract]

Inventory

Note 6 – Inventory

At December 31, 2016 and 2015, inventory was comprised of the following:

(In thousands)	2016		2015
Raw materials	$	40,461	$	34,223
Work in process		4,003		2,893
Finished goods		60,653		54,417
Total Inventory, net	$	105,117	$	91,533

We establish reserves for estimated excess, obsolete, or unmarketable inventory equal to the difference between the cost of the inventory and the estimated fair value of the inventory based upon assumptions about future demand and market conditions. At December 31, 2016 and 2015, raw materials reserves totaled $14.6 million and $17.5 million, respectively, and finished goods inventory reserves totaled $10.6 million and $9.2 million, respectively.

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Property, Plant and Equipment

12 Months Ended

Dec. 31, 2016

Property Plant And Equipment [Abstract]

Property, Plant and Equipment

Note 7 – Property, Plant and Equipment

At December 31, 2016 and 2015, property, plant and equipment were comprised of the following:

(In thousands)	2016			2015
Land	$	4,575		$	4,575
Building and land improvements		29,229			25,667
Building		68,301			68,301
Furniture and fixtures		18,477			17,347
Computer hardware and software		87,655			76,389
Engineering and other equipment		118,746			112,132
Total Property, Plant and Equipment		326,983			304,411
Less accumulated depreciation		(242,514	)		(231,178	)
Total Property, Plant and Equipment, net	$	84,469		$	73,233

Depreciation expense was $12.0 million, $12.3 million and $12.5 million in 2016, 2015, and 2014, respectively.

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Goodwill and Intangible Assets

12 Months Ended

Dec. 31, 2016

Goodwill And Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets

Note 8 – Goodwill and Intangible Assets

Goodwill was $3.5 million at December 31, 2016 and 2015, and was previously recorded in our Enterprise Networks reportable segment. As a result of our new reporting structure adopted in the first quarter of 2016, which is discussed further in Note 12, we reallocated goodwill from our Enterprise Networks reportable segment to our two, new reportable segments – Network Solutions and Services & Support. As a result, goodwill of $3.1 million and $0.4 million was reallocated to our Network Solutions and Services & Support reportable segments, respectively.

We evaluate the carrying value of goodwill during the fourth quarter of each year and between annual evaluations if events occur or circumstances change that would more likely than not reduce the fair value of the reporting unit below its carrying amount. We have elected to first assess the qualitative factors to determine whether it is more likely than not that the fair value of the reporting unit to which the goodwill is assigned is less than its carrying amount as a basis for determining whether it is necessary to perform the two-step impairment test. If we determine that it is more likely than not that its fair value is less than its carrying amount, then the two-step impairment test will be performed. Based on the results of our qualitative assessment in 2016, we concluded that it was not necessary to perform the two-step impairment test. There have been no impairment losses recognized since the acquisition in 2011.

Intangible assets are included in other assets in the accompanying Consolidated Balance Sheets. The following table presents our intangible assets as of December 31, 2016 and 2015:

(In thousands)	2016							2015
	Gross Value		Accumulated Amortization			Net Value		Gross Value		Accumulated Amortization			Net Value
Customer relationships	$	6,899	$	(3,208	)	$	3,691	$	5,828	$	(2,627	)	$	3,201
Developed technology		6,444		(5,061	)		1,383		5,720		(4,329	)		1,391
Intellectual property		2,340		(2,129	)		211		2,340		(1,854	)		486
Supply agreement		1,400		(544	)		856		—		—			—
License		500		(113	)		387		—		—			—
Patent		500		(20	)		480		—		—			—
Trade names		370		(285	)		85		270		(265	)		5
Non-compete		200		(26	)		174		11		(11	)		—
Total	$	18,653	$	(11,386	)	$	7,267	$	14,169	$	(9,086	)	$	5,083

Amortization expense was $2.5 million, $1.9 million and $2.3 million for the years ended December 31, 2016, 2015 and 2014, respectively.

As of December 31, 2016, the estimated future amortization expense of intangible assets is as follows:

(In thousands)	Amount
2017	$	2,867
2018		1,168
2019		655
2020		621
2021		568
Thereafter		1,388
Total	$	7,267

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Alabama State Industrial Development Authority Financing and Economic Incentives

12 Months Ended

Dec. 31, 2016

Text Block [Abstract]

Alabama State Industrial Development Authority Financing and Economic Incentives

Note 9 – Alabama State Industrial Development Authority Financing and Economic Incentives

In conjunction with an expansion of our Huntsville, Alabama, facility, we were approved for participation in an incentive program offered by the State of Alabama Industrial Development Authority (the “Authority”). Pursuant to the program, on January 13, 1995, the Authority issued $20.0 million of its taxable revenue bonds and loaned the proceeds from the sale of the bonds to ADTRAN. The bonds were originally purchased by AmSouth Bank of Alabama, Birmingham, Alabama (the “Bank”). Wachovia Bank, N.A., Nashville, Tennessee (formerly First Union National Bank of Tennessee) (the “Bondholder”), which was acquired by Wells Fargo & Company on December 31, 2008, purchased the original bonds from the Bank and made further advances to the Authority, bringing the total amount outstanding to $50.0 million. An Amended and Restated Taxable Revenue Bond (“Amended and Restated Bond”) was issued and the original financing agreement was amended. The Amended and Restated Bond bears interest, payable monthly. The interest rate is 2% per annum. The Amended and Restated Bond matures on January 1, 2020, and is currently outstanding in the aggregate principal amount of $27.8 million. The estimated fair value of the bond using a level 2 valuation technique at December 31, 2016 was approximately $28.1 million, based on a debt security with a comparable interest rate and maturity and a Standard & Poor’s credit rating of AAA. We are required to make payments to the Authority in amounts necessary to pay the interest on the Amended and Restated Bond. Included in long-term investments at December 31, 2016 is $27.8 million which is invested in a restricted certificate of deposit. These funds serve as a collateral deposit against the principal of this bond, and we have the right to set-off the balance of the Bond with the collateral deposit in order to reduce the balance of the indebtedness.

In conjunction with this program, we are eligible to receive certain economic incentives from the state of Alabama that reduce the amount of payroll withholdings that we are required to remit to the state for those employment positions that qualify under the program. We realized economic incentives related to payroll withholdings totaling $1.3 million for each of the years ended December 31, 2016, 2015 and 2014.

We made principal payments of $1.1 million for the years ended December 31, 2016 and 2015, respectively, and anticipate making a principal payment in 2017.  At December 31, 2016, $1.0 million of the bond debt was classified as a current liability in accounts payable in the Consolidated Balance Sheets.

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Income Taxes

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Income Taxes

Note 10 – Income Taxes

A summary of the components of the provision for income taxes for the years ended December 31, 2016, 2015 and 2014 is as follows:

(In thousands)	2016			2015			2014
Current
Federal	$	12,733		$	7,504		$	7,626
State		1,141			279			599
International		477			(29	)		12,587
Total Current		14,351			7,754			20,812
Deferred
Federal		647			(585	)		(1,083	)
State		73			(66	)		(123	)
International		(3,405	)		(41	)		(4,320	)
Total Deferred		(2,685	)		(692	)		(5,526	)
Total Provision for Income Taxes	$	11,666		$	7,062		$	15,286

Our effective income tax rate differs from the federal statutory rate due to the following:

	2016			2015			2014
Tax provision computed at the federal statutory rate		35.00	%		35.00	%		35.00	%
State income tax provision, net of federal benefit		3.93			4.86			2.69
Federal research credits		(8.15	)		(12.55	)		(4.05	)
Foreign taxes		(0.34	)		2.10			(7.26	)
Tax-exempt income		(0.53	)		(1.94	)		(1.25	)
State tax incentives		(2.77	)		(5.04	)		(2.21	)
Stock-based compensation		2.53			6.91			3.06
Domestic production activity deduction		(2.23	)		(3.17	)		(1.15	)
Bargain purchase		(2.64	)		—			—
Other, net		0.08			1.30			0.69
Effective Tax Rate		24.88	%		27.47	%		25.52	%

Income before provision for income taxes for the years ended December 31, 2016, 2015 and 2014 is as follows:

(In thousands)	2016			2015			2014
U.S. entities	$	54,077		$	27,400		$	23,812
International entities		(7,182	)		(1,692	)		36,094
Total	$	46,895		$	25,708		$	59,906

Income before provision for income taxes for international entities reflects income based on statutory transfer pricing agreements. This amount does not correlate to consolidated international revenues, many of which occur from our U.S. entity.

Deferred income taxes on the balance sheet result from temporary differences between the amount of assets and liabilities recognized for financial reporting and tax purposes. The principal components of our current and non-current deferred taxes are as follows:

(In thousands)	2016			2015
Deferred tax assets
Accounts receivable	$	—		$	7
Inventory		12,020			12,558
Accrued expenses		5,551			6,359
Investments		1,062			—
Deferred compensation		5,751			5,072
Stock-based compensation		4,724			4,704
Uncertain tax positions related to state taxes and related interest		762			1,026
Pensions		4,273			5,729
Foreign losses		6,486			5,389
State losses and credit carry-forwards		4,021			4,187
Federal loss and research carry-forwards		5,886			5,886
Valuation allowance		(6,149	)		(7,250	)
Total Deferred Tax Assets		44,387			43,667
Deferred tax liabilities
Property, plant and equipment		(4,433	)		(3,315	)
Accrued expenses		—			(2,791	)
Intellectual property		(1,918	)		(476	)
Investments		—			(70	)
Total Deferred Tax Liabilities		(6,351	)		(6,652	)
Net Deferred Tax Assets	$	38,036		$	37,015

At December 31, 2016 and 2015, non-current deferred taxes related to our investments and our defined benefit pension plan, reflect deferred taxes on the net unrealized gains on available-for-sale investments and deferred taxes on unrealized losses in our pension plan. The net change in non-current deferred taxes associated with these items, a deferred tax benefit of $1.5 million and $3.7 million in 2016 and 2015, respectively, is recorded as an adjustment to other comprehensive income, presented in the Consolidated Statements of Comprehensive Income.

Based upon our results of operations in 2016 and expected profitability in future years in a certain international jurisdiction, we concluded that it is more likely than not certain foreign deferred tax assets will be realized. As of December 31, 2016, the remaining valuation allowance primarily relates to deferred tax assets related to state credit carry-forwards from tax credits in excess of our annual tax liability to an individual state where we do not generate sufficient state income to offset the credit and net operating losses in foreign jurisdictions. We believe it is more likely than not that we will not realize the full benefits of the deferred tax assets arising from these losses and credits, and accordingly, we have provided a valuation allowance against these deferred tax assets. The deferred tax assets for foreign and domestic carry-forwards, unamortized research and development costs, and state credit carry-forwards of $16.4 million will expire between 2017 and 2030. The loss carry-forwards were acquired through acquisitions in 2009 and 2011. We will continue to assess the realization of our deferred tax assets and related valuations allowances. We do not provide for U.S. income tax on undistributed earnings of our foreign operations, whose earnings are intended to be permanently reinvested. These earnings are not required to service debt or fund our U.S. operations. It is impracticable to determine the amount of any unrecognized deferred tax liability for temporary differences related to investments in foreign subsidiaries. The net change in our valuation allowance from December 31, 2015 to December 31, 2016 was $1.1 million.

As of December 31, 2016 and 2015, respectively, our cash and cash equivalents were $79.9 million and $84.6 million and short-term investments were $43.2 million and $34.4 million, which provided an available short-term liquidity of $123.1 million and $118.9 million.  Of these amounts, our foreign subsidiaries held cash of $42.1 million and $38.9 million, respectively, representing approximately 34.2% and 32.7% of available short-term liquidity, which is used to fund on-going liquidity needs of these subsidiaries.  We intend to permanently reinvest these funds outside the U.S. and our current business plans do not indicate a need to repatriate to fund domestic operations.  However, if these funds were repatriated to the U.S. or used for U.S. operations, certain amounts related to the earnings and profits of foreign subsidiaries could be subject to U.S. tax for the incremental amount in excess of the foreign tax paid.  Due to the timing and circumstances of repatriation of such earnings, if any, it is not practical to determine the amount of funds subject to repatriation or the associated unrecognized deferred tax liability related to the amount.

During 2016, 2015 and 2014, we recorded an income tax benefit (expense) of nil, $(40) thousand and $0.1 million, respectively, as an adjustment to equity. This is calculated on the difference between the exercise price of stock option exercises and the market price of the underlying common stock upon exercise.

The change in the unrecognized income tax benefits for the years ended December 31, 2016, 2015 and 2014 is reconciled below:

(In thousands)	2016			2015			2014
Balance at beginning of period	$	2,537		$	3,334		$	3,240
Increases for tax position related to:
Prior years		95			—			—
Current year		428			280			522
Decreases for tax positions related to:
Prior years		—			(29	)		—
Settlements with taxing authorities		—			(103	)		—
Expiration of applicable statute of limitations		(834	)		(945	)		(428	)
Balance at end of period	$	2,226		$	2,537		$	3,334

As of December 31, 2016, 2015, and 2014, our total liability for unrecognized tax benefits was $2.2 million, $2.5 million, and $3.3 million, respectively, of which $1.7 million, $1.8 million, and $2.6 million, respectively, would reduce our effective tax rate if we were successful in upholding all of the uncertain positions and recognized the amounts recorded. We classify interest and penalties recognized on the liability for unrecognized tax benefits as income tax expense. As of December 31, 2016, 2015 and 2014, the balances of accrued interest and penalties were $0.8 million, $0.9 million and $1.0 million, respectively.

We do not anticipate a single tax position generating a significant increase or decrease in our liability for unrecognized tax benefits within 12 months of this reporting date. We file income tax returns in the U.S. federal and various state jurisdictions and several foreign jurisdictions. We are not currently under audit by the Internal Revenue Service. Generally, we are not subject to changes in income taxes by any taxing jurisdiction for the years prior to 2013.

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Employee Benefit Plans

12 Months Ended

Dec. 31, 2016

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plans

Note 11 – Employee Benefit Plans

Pension Benefit Plan

We maintain a defined benefit pension plan covering employees in certain foreign countries.

The pension benefit plan obligations and funded status at December 31, 2016 and 2015, are as follows:

(In thousands)	2016			2015
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	$	(26,851	)	$	(30,507	)
Service cost		(1,211	)		(1,314	)
Interest cost		(720	)		(615	)
Actuarial gain (loss) - experience		431			247
Actuarial gain (loss) - assumptions		(2,628	)		2,078
Benefit payments		52			81
Effects of foreign currency exchange rate changes		916			3,179
Projected benefit obligation at end of period		(30,011	)		(26,851	)
Change in plan assets:
Fair value of plan assets at beginning of period		19,213			20,338
Actual return on plan assets		1,494			988
Effects of foreign currency exchange rate changes		(662	)		(2,113	)
Fair value of plan assets at end of period		20,045			19,213
Funded (unfunded) status at end of period	$	(9,966	)	$	(7,638	)

The accumulated benefit obligation was $28.7 million and $25.1 million at December 31, 2016 and 2015, respectively. The increase in the accumulated benefit obligation and the change in actuarial gain (loss) is primarily attributable to a decrease in the discount rate used in 2016 to determine the accumulated benefit obligation.

The net amounts recognized in the balance sheet for the unfunded pension liability as of December 31, 2016 and 2015 are as follows:

(In thousands)	2016			2015
Current liability	$	—		$	—
Non-current liability		(9,966	)		(7,638	)
Total	$	(9,966	)	$	(7,638	)

The components of net periodic pension cost and amounts recognized in other comprehensive income for the years ended December 31, 2016, 2015 and 2014 are as follows:

(In thousands)	2016			2015			2014
Net periodic benefit cost:
Service cost	$	1,211		$	1,314		$	1,189
Interest cost		720			615			836
Expected return on plan assets		(1,057	)		(1,011	)		(1,086	)
Amortization of actuarial losses		175			407			—
Net periodic benefit cost		1,049			1,325			939
Other changes in plan assets and benefit obligations    recognized in other comprehensive income:
Net actuarial (gain) loss		1,782			(2,303	)		7,052
Amortization of actuarial losses		(156	)		(396	)		—
Amount recognized in other comprehensive income		1,626			(2,699	)		7,052
Total recognized in net periodic benefit cost and other    comprehensive income	$	2,675		$	(1,374	)	$	7,991

The amounts recognized in accumulated other comprehensive income as of December 31, 2016 and 2015 are as follows:

(In thousands)	2016		2015
Net actuarial loss	$	6,871	$	5,245

The defined benefit pension plan is accounted for on an actuarial basis, which requires the selection of various assumptions, including an expected rate of return on plan assets and a discount rate. The expected return on our German plan assets that is utilized in determining the benefit obligation and net periodic benefit cost is derived from periodic studies, which include a review of asset allocation strategies, anticipated future long-term performance of individual asset classes, risks using standard deviations and correlations of returns among the asset classes that comprise the plans' asset mix. While the studies give appropriate consideration to recent plan performance and historical returns, the assumptions are primarily long-term, prospective rates of return.

Another key assumption in determining net pension expense is the assumed discount rate to be used to discount plan obligations. The discount rate has been derived from the returns of high-quality, corporate bonds denominated in Euro currency with durations close to the duration of our pension obligations.

The weighted-average assumptions that were used to determine the net periodic benefit cost for the years ended December 31, 2016, 2015 and 2014 are as follows:

	2016			2015			2014
Discount rates		2.64	%		2.20	%		3.70	%
Rate of compensation increase		2.00	%		2.25	%		2.25	%
Expected long-term rates of return		5.40	%		5.40	%		5.40	%

The weighted-average assumptions that were used to determine the benefit obligation at December 31, 2016 and 2015:

	2016			2015
Discount rates		1.90	%		2.64	%
Rate of compensation increase		2.00	%		2.25	%

Actuarial gains and losses are recorded in accumulated other comprehensive income. To the extent unamortized gains and losses exceed 10% of the higher of the market-related value of assets or the projected benefit obligation, the excess is amortized as a component of net periodic pension cost over the remaining service period of active participants. We estimate that $0.3 million will be amortized from accumulated other comprehensive income into net periodic pension cost in 2017 for the net actuarial loss.

We do not anticipate making a contribution to this pension plan in 2017. The following pension benefit payments, which reflect expected future service, as appropriate, are expected to be paid to participants:

(In thousands)
2017	$	348
2018		515
2019		699
2020		964
2021		1,079
2022 – 2026		5,156
Total	$	8,761

We have categorized our cash equivalents and our investments held at fair value into a three-level fair value hierarchy based on the priority of the inputs to the valuation technique for the cash equivalents and investments as follows: Level 1 - Values based on unadjusted quoted prices for identical assets or liabilities in an active market; Level 2 - Values based on quoted prices in markets that are not active or model inputs that are observable either directly or indirectly; Level 3 - Values based on prices or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs include information supplied by investees.

	Fair Value Measurements at December 31, 2016 Using
(In thousands)	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents	$	6	$	6	$	—	$	—
Available-for-sale securities
Bond funds:
Corporate bonds		12,546		12,546		—		—
Government bonds		2,037		2,037		—		—
Equity funds:
Large cap blend		4,462		4,462		—		—
Large cap value		249		249		—		—
Balanced fund		745		745		—		—
Available-for-sale securities		20,039		20,039		—		—
Total	$	20,045	$	20,045	$	—	$	—

	Fair Value Measurements at December 31, 2015 Using
(In thousands)	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents	$	3	$	3	$	—	$	—
Available-for-sale securities
Bond funds:
Corporate bonds		11,633		11,633		—		—
Government bonds		1,960		1,960		—		—
Equity funds:
Large cap blend		4,604		4,604		—		—
Large cap value		258		258		—		—
Balanced fund		755		755		—		—
Available-for-sale securities		19,210		19,210		—		—
Total	$	19,213	$	19,213	$	—	$	—

Our investment policy includes various guidelines and procedures designed to ensure assets are invested in a manner necessary to meet expected future benefits earned by participants, and consider a broad range of economic conditions. Central to the policy are target allocation ranges by asset class, which is currently 75% for bond funds and 25% for equity funds.

The objectives of the target allocations are to maintain investment portfolios that diversify risk through prudent asset allocation parameters, achieve asset returns that meet or exceed the plans’ actuarial assumptions, and achieve asset returns that are competitive with like institutions employing similar investment strategies.

The investment policy is periodically reviewed by us and a designated third-party fiduciary for investment matters. The policy is established and administered in a manner that is compliant at all times with applicable government regulations.

401(k) Savings Plan

We maintain the ADTRAN, Inc. 401(k) Retirement Plan (Savings Plan) for the benefit of our eligible employees. The Savings Plan is intended to qualify under Sections 401(a) and 401(k) of the Internal Revenue Code of 1986, as amended (Code), and is intended to be a “safe harbor” 401(k) plan under Code Section 401(k)(12). The Savings Plan allows employees to save for retirement by contributing part of their compensation to the plan on a tax-deferred basis. The Savings Plan also requires us to contribute a “safe harbor” amount each year. We match up to 4% of employee contributions (100% of an employee’s first 3% of contributions and 50% of their next 2% of contributions), beginning on the employee’s one year anniversary date. In calculating our matching contribution, we only use compensation up to the statutory maximum under the Code ($265 thousand for 2016). All contributions under the Savings Plan are 100% vested. Expenses recorded for employer contributions and plan administration costs for the Savings Plan amounted to approximately $4.1 million, $4.7 million and $4.5 million in 2016, 2015 and 2014, respectively.

Deferred Compensation Plans

We maintain four deferred compensation programs for certain executive management employees and our Board of Directors.

For our executive management employees, the ADTRAN, Inc. Deferred Compensation Program for Employees is offered as a supplement to our tax-qualified 401(k) plan and is available to certain executive management employees who have been designated by our Board of Directors. This deferred compensation plan allows participants to defer all or a portion of certain specified bonuses and up to 25% of remaining cash compensation, and permits us to make matching contributions on a discretionary basis, without the limitations that apply to the 401(k) plan. To date, we have not made any matching contributions under this plan. We also maintain the ADTRAN, Inc. Equity Deferral Program for Employees. Under this plan, participants may elect to defer all or a portion of their vested PSUs to the Plan. Such deferrals shall continue to be held and deemed to be invested in shares of ADTRAN stock unless and until the amounts are distributed or such deferrals are moved to another deemed investment pursuant to an election made by the Participant.

For our Board of Directors, we maintain the ADTRAN, Inc. Deferred Compensation Program for Directors. This program allows our Board of Directors to defer all or a portion of monetary remuneration paid to the Director, including, but not limited to, meeting fees and annual retainers. We also maintain the ADTRAN, Inc. Equity Deferral Program for Directors. Under this plan, participants may elect to defer all or a portion of their vested restricted stock awards. Such deferrals shall continue to be held and deemed to be invested in shares of ADTRAN stock unless and until the amounts are distributed or such deferrals are moved to another deemed investment pursuant to an election made by the Director.

We have set aside the plan assets for all plans in a rabbi trust (Trust) and all contributions are credited to bookkeeping accounts for the participants. The Trust assets are subject to the claims of our creditors in the event of bankruptcy or insolvency. The assets of the Trust are deemed to be invested in pre-approved mutual funds as directed by each participant, and the participant’s bookkeeping account is credited with the earnings and losses attributable to those investments. Benefits are scheduled to be distributed six months after termination of employment in a single lump sum payment or annual installments paid over a three or ten year term. Distributions will be made on a pro rata basis from each of the hypothetical investments of the Participant’s account in cash. Any whole shares of ADTRAN, Inc. common stock that are distributed will be distributed in-kind.

Assets of the Trust are deemed invested in mutual funds that cover an investment spectrum ranging from equities to money market instruments. These mutual funds are publicly quoted and reported at fair value. The fair value of the assets held by the Trust and the amounts payable to the plan participants at December 31, 2016 and 2015 are as follows:

(In thousands)	2016		2015
Fair Value of Plan Assets
Long-term Investments	$	14,596	$	12,834
Total Fair Value of Plan Assets	$	14,596	$	12,834
Amounts Payable to Plan Participants
Non-current Liabilities	$	14,596	$	12,834
Total Amounts Payable to Plan Participants	$	14,596	$	12,834

Interest and dividend income of the Trust have been included in interest and dividend income in the accompanying 2016, 2015 and 2014 Consolidated Statements of Income. Changes in the fair value of the plan assets held by the Trust have been included in accumulated other comprehensive income in the accompanying 2016 and 2015 Consolidated Balance Sheets. Changes in the fair value of the deferred compensation liability are included as selling, general and administrative expense in the accompanying 2016, 2015 and 2014 Consolidated Statements of Income. Based on the changes in the total fair value of the Trust’s assets, we recorded deferred compensation income (expense) in 2016, 2015 and 2014 of $(1.3) million, $0.3 million and $(0.7) million, respectively.

Retiree Medical Coverage

We provide medical, dental and prescription drug coverage to one retired former officer and his spouse, for his life, on the same terms as provided to our active officers, and to the spouse of a former deceased officer for up to 30 years. At December 31, 2016 and 2015, this liability totaled $0.2 million.

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Segment Information and Major Customers

12 Months Ended

Dec. 31, 2016

Segment Reporting [Abstract]

Segment Information and Major Customers

Note 12 – Segment Information and Major Customers

In 2015, we realigned our organizational structure to better match our market opportunities, technological development initiatives, and improve efficiencies. During the first quarter of 2016, our chief operating decision maker requested changes in the information that he regularly reviews for purposes of allocating resources and assessing performance. As a result, beginning with the quarter ended March 31, 2016, we began reporting our financial performance based on two, new reportable segments – Network Solutions and Services & Support. Network Solutions includes hardware products and next-generation virtualized solutions used in service provider or business networks, as well as prior-generation products. Services & Support includes our suite of ProCloud managed services, network installation, engineering and maintenance services, and fee-based technical support and equipment repair/replacement plans.

We evaluate the performance of our new segments based on gross profit; therefore, selling, general and administrative expenses, research and development expenses, interest and dividend income, interest expense, net realized investment gain/loss, other income/expense and provision for taxes are reported on a company-wide, functional basis only. Historical financial information by reportable segment and category, as discussed below, has been recast to conform to our new reporting structure. There are no inter-segment revenues.

The following table presents information about the reported sales and gross profit of our reportable segments for each of the years ended December 31, 2016, 2015 and 2014. Asset information by reportable segment is not reported, since we do not produce such information internally.

Sales and Gross Profit by Market Segment
(In thousands)	2016				2015				2014
	Sales		Gross Profit		Sales		Gross Profit		Sales		Gross Profit
Network Solutions	$	525,502	$	254,807	$	527,422	$	233,579	$	559,532	$	271,517
Services & Support		111,279		36,537		72,642		33,318		70,475		39,810
Total	$	636,781	$	291,344	$	600,064	$	266,897	$	630,007	$	311,327

Sales by Category

In addition to our new reporting segments, we will also report revenue for the following three categories – Access & Aggregation, Customer Devices, and Traditional & Other Products.

The table below presents sales information by product category for the years ended December 31, 2016, 2015 and 2014:

(In thousands)	2016		2015		2014
Access & Aggregation	$	436,372	$	405,698	$	401,769
Customer Devices		137,608		125,565		138,051
Traditional & Other Products		62,801		68,801		90,187
Total	$	636,781	$	600,064	$	630,007

The following table presents sales information by geographic area for the years ended December 31, 2016, 2015 and 2014. International sales correlate to shipments with a non-U.S. destination.

(In thousands)	2016		2015		2014
United States	$	501,337	$	419,366	$	381,382
Germany		85,780		111,666		150,987
Other international		49,664		69,032		97,638
Total	$	636,781	$	600,064	$	630,007

Customers comprising more than 10% of revenue can change from year to year. Single customers comprising more than 10% of our revenue in 2016 included three customers at 24%, 19% and 12%. Single customers comprising more than 10% of our revenue in 2015 included three customers at 20%, 17% and 14%. Single customers comprising more than 10% of our revenue in 2014 included two customers at 21% and 14%. No other customer accounted for 10% or more of our sales in 2016, 2015 or 2014. Our five largest customers, other than those with more than 10 percent of revenues disclosed above, can change from year to year.  These customers represented 13%, 14%, and 22% of total revenue in 2016, 2015 and 2014, respectively. Revenues in this disclosure do not include distributor agents, who predominately provide fulfillment services to end users. In such cases where known, that revenue is associated with the end user.

Additional Segment Information

As of December 31, 2016, long-lived assets, net totaled $84.5 million, which includes $79.9 million held in the United States and $4.6 million held outside the United States. As of December 31, 2015, long-lived assets, net totaled $73.2 million, which includes $68.8 million held in the United States and $4.4 million held outside the United States.

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Commitments and Contingencies

12 Months Ended

Dec. 31, 2016

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 13 – Commitments and Contingencies

In the ordinary course of business, we may be subject to various legal proceedings and claims, including employment disputes, patent claims, disputes over contract agreements and other commercial disputes. In some cases, claimants seek damages or other relief, such as royalty payments related to patents, which, if granted, could require significant expenditures. Although the outcome of any claim or litigation can never be certain, it is our opinion that the outcome of all contingencies of which we are currently aware will not materially affect our business, operations, financial condition or cash flows.

We have committed to invest up to an aggregate of $7.9 million in two private equity funds, and we have contributed $8.4 million as of December 31, 2016, of which $7.7 million has been applied to these commitments.

We lease office space and equipment under operating leases which expire at various dates through 2025. As of December 31, 2016, future minimum rental payments under non-cancelable operating leases with original maturities of greater than 12 months are as follows:

(In thousands)
2017	$	3,788
2018		2,043
2019		847
2020		741
Thereafter		3,243
Total	$	10,662

Rental expense was $4.2 million, $4.9 million and $4.7 million for the years ended December 31, 2016, 2015 and 2014, respectively.

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Earnings per Share

12 Months Ended

Dec. 31, 2016

Earnings Per Share [Abstract]

Earnings per Share

Note 14 – Earnings per Share

A summary of the calculation of basic and diluted earnings per share (EPS) for the years ended December 31, 2016, 2015 and 2014 is as follows:

(In thousands, except for per share amounts)	2016		2015		2014
Numerator
Net Income	$	35,229	$	18,646	$	44,620
Denominator
Weighted average number of shares – basic		48,724		51,145		55,120
Effect of dilutive securities:
Stock options		170		81		304
Restricted stock and restricted stock units		55		41		58
Weighted average number of shares – diluted	$	48,949	$	51,267	$	55,482
Net income per share – basic	$	0.72	$	0.36	$	0.81
Net income per share – diluted	$	0.72	$	0.36	$	0.80

For each of the years ended December 31, 2016, 2015 and 2014, 4.6 million, 6.1 million and 4.4 million stock options were outstanding but were not included in the computation of that year’s diluted EPS because the options’ exercise prices were greater than the average market price of the common shares, therefore making them anti-dilutive under the treasury stock method.

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Summarized Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Summarized Quarterly Financial Data (Unaudited)

Note 15 – Summarized Quarterly Financial Data (Unaudited)

The following table presents unaudited quarterly operating results for each of our last eight fiscal quarters. This information has been prepared on a basis consistent with our audited financial statements and includes all adjustments, consisting only of normal recurring adjustments, considered necessary for a fair presentation of the data.

Unaudited Quarterly Operating Results

(In thousands, except for per share amounts)

Three Months Ended	March 31, 2016		June 30, 2016		September 30, 2016		December 31, 2016
Net sales	$	142,204	$	162,701	$	168,890	$	162,986
Gross profit	$	65,794	$	78,955	$	75,808	$	70,787
Operating income	$	5,521	$	14,812	$	10,130	$	4,272
Net income	$	5,014	$	10,228	$	12,415	$	7,572
Earnings per common share	$	0.10	$	0.21	$	0.26	$	0.16
Earnings per common share assuming dilution (1)	$	0.10	$	0.21	$	0.26	$	0.16

Three Months Ended	March 31, 2015		June 30, 2015		September 30, 2015		December 31, 2015
Net sales	$	142,835	$	160,138	$	158,078	$	139,013
Gross profit	$	65,563	$	68,246	$	70,649	$	62,439
Operating income	$	1,963	$	644	$	8,072	$	2,800
Net income	$	3,317	$	2,544	$	7,067	$	5,718
Earnings per common share	$	0.06	$	0.05	$	0.14	$	0.12
Earnings per common share assuming dilution (1)	$	0.06	$	0.05	$	0.14	$	0.12

⁽¹⁾ Assumes exercise of dilutive stock options calculated under the treasury stock method.

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Related Party Transactions

12 Months Ended

Dec. 31, 2016

Related Party Transactions [Abstract]

Related Party Transactions

Note 16 – Related Party Transactions

We employed the law firm of our director emeritus for legal services. All bills for services rendered by this firm were reviewed and approved by our Chief Financial Officer. We believe that the fees for such services are comparable to those charged by other firms for services rendered to us. The services of our director emeritus ended with his death on September 7, 2014. For the year ended 2014, we incurred fees of $0.1 million for these legal services.

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Subsequent Events

12 Months Ended

Dec. 31, 2016

Subsequent Events [Abstract]

Subsequent Events

Note 17 – Subsequent Events

On January 17, 2017, the Board declared a quarterly cash dividend of $0.09 per common share to be paid to shareholders of record at the close of business on February 2, 2017. The quarterly dividend payment was $4.4 million and was paid on February 16, 2017. In July 2003, our Board of Directors elected to begin declaring quarterly dividends on our common stock considering the tax treatment of dividends and adequate levels of Company liquidity.

During the first quarter and as of February 24, 2017, we have repurchased 0.2 million shares of our common stock through open market purchases at an average cost of $21.46 per share. We currently have the authority to purchase an additional 4.2 million shares of our common stock under the current plan approved by the Board of Directors.

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Schedule II - Valuation and Qualifying Accounts

12 Months Ended

Dec. 31, 2016

Valuation And Qualifying Accounts [Abstract]

Schedule II - Valuation and Qualifying Accounts

SCHEDULE II

VALUATION AND QUALIFYING ACCOUNTS

Column A	Column B		Column C		Column D		Column E
(In thousands)	Balance at Beginning of Period		Charged to Costs & Expenses		Deductions		Balance at End of Period
Year ended December 31, 2016
Allowance for Doubtful Accounts	$	19		—		19	$	—
Inventory Reserve	$	26,675		3,303		4,729	$	25,249
Warranty Liability	$	8,739		8,561		8,752	$	8,548
Deferred Tax Asset Valuation Allowance	$	7,250		69		1,170	$	6,149
Year ended December 31, 2015
Allowance for Doubtful Accounts	$	136		19		136	$	19
Inventory Reserve	$	24,682		2,225		232	$	26,675
Warranty Liability	$	8,415		2,998		2,674	$	8,739
Deferred Tax Asset Valuation Allowance	$	7,463		81		294	$	7,250
Year ended December 31, 2014
Allowance for Doubtful Accounts	$	130		23		17	$	136
Inventory Reserve	$	22,993		2,549		860	$	24,682
Warranty Liability	$	8,977		3,103		3,665	$	8,415
Deferred Tax Asset Valuation Allowance	$	8,842		283		1,662	$	7,463

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Nature of Business and Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2016

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Principles of Consolidation

Principles of Consolidation

Our consolidated financial statements include ADTRAN and its wholly owned subsidiaries. All inter-company accounts and transactions have been eliminated in consolidation.

Use of Estimates

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expense during the reporting period. Our more significant estimates include the obsolete and excess inventory reserves, warranty reserves, customer rebates, determination of the deferred revenue components of multiple element sales agreements, estimated costs to complete obligations associated with deferred revenues and network installations, estimated income tax provision and income tax contingencies, the fair value of stock- based compensation, impairment of goodwill, valuation and estimated lives of intangible assets, estimated pension liability, fair value of investments, and the evaluation of other-than-temporary declines in the value of investments. Actual amounts could differ significantly from these estimates.

Cash and Cash Equivalents

Cash and Cash Equivalents

Cash and cash equivalents represent demand deposits, money market funds, and short-term investments classified as available-for-sale with original maturities of three months or less. We maintain depository investments with certain financial institutions. Although these depository investments may exceed government insured depository limits, we have evaluated the credit worthiness of these applicable financial institutions, and determined the risk of material financial loss due to the exposure of such credit risk to be minimal. As of December 31, 2016, $77.9 million of our cash and cash equivalents, primarily certain domestic money market funds and foreign depository accounts, were in excess of government provided insured depository limits.

Financial Instruments

Financial Instruments

The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents, accounts receivable, and accounts payable approximate fair value due to the immediate or short-term maturity of these financial instruments. The carrying amount reported for bonds payable was $27.8 million, compared to an estimated fair value of $28.1 million, based on a debt security with a comparable interest rate and maturity and a Standard & Poor’s credit rating of AAA.

Investments with contractual maturities beyond one year, such as our variable rate demand notes, may be classified as short-term based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. Despite the long-term nature of their stated contractual maturities, we routinely buy and sell these securities and we believe we have the ability to quickly sell them to the remarketing agent, tender agent, or issuer at par value plus accrued interest in the event we decide to liquidate our investment in a particular variable rate demand note. All income generated from these investments was recorded as interest income. We have not been required to record any losses relating to variable rate demand notes.

Long-term investments represent a restricted certificate of deposit held at cost, deferred compensation plan assets, corporate bonds, municipal fixed-rate bonds, asset-backed bonds, mortgage/agency backed bonds, U.S. and foreign government bonds, variable rate demand notes, marketable equity securities, and other equity investments. Marketable equity securities are reported at fair value as determined by the most recently traded price of the securities at the balance sheet date, although the securities may not be readily marketable due to the size of the available market. Unrealized gains and losses, net of tax, are reported as a separate component of stockholders’ equity. Realized gains and losses on sales of securities are computed under the specific identification method and are included in current income. We review our investment portfolio quarterly for investments considered to have sustained an other-than-temporary decline in value. Impairment charges for other-than-temporary declines in value are recorded as realized losses in the accompanying consolidated statements of income. All of our investments at December 31, 2016 and 2015 are classified as available-for-sale securities. See Note 4 of Notes to Consolidated Financial Statements for additional information.

Accounts Receivable

Accounts Receivable

We record accounts receivable at net realizable value. Prior to establishing payment terms for a new customer, we evaluate the credit risk of the customer. Credit limits and payment terms established for new customers are re-evaluated periodically based on customer collection experience and other financial factors. At December 31, 2016, three customers accounted for 63.3% of our total accounts receivable. At December 31, 2015, three customers accounted for 37.3% of our total accounts receivable.

We maintain an allowance for doubtful accounts for losses resulting from the inability of our customers to make required payments. We regularly review the allowance for doubtful accounts and consider factors such as the age of accounts receivable balances, the current economic conditions that may affect a customer’s ability to pay, significant one-time events and our historical experience. If the financial condition of a customer deteriorates, resulting in an impairment of their ability to make payments, we may be required to record an allowance for doubtful accounts. If circumstances change with regard to individual receivable balances that have previously been determined to be uncollectible (and for which a specific reserve has been established), a reduction in our allowance for doubtful accounts may be required. Our allowance for doubtful accounts was nil and $19 thousand at December 31, 2016 and December 31, 2015, respectively.

Other Receivables

Other Receivables

Other receivables are comprised primarily of amounts due from subcontract manufacturers for product component transfers, accrued interest on investments and on a restricted certificate of deposit, amounts due from various jurisdictions for value-added tax, and amounts due from employee stock option exercises.

Inventory

Inventory

Inventory is carried at the lower of cost or market, with cost being determined using the first-in, first-out method. Standard costs for material, labor and manufacturing overhead are used to value inventory. Standard costs are updated at least quarterly; therefore, inventory costs approximate actual costs at the end of each reporting period. We establish reserves for estimated excess, obsolete or unmarketable inventory equal to the difference between the cost of the inventory and the estimated fair value of the inventory based upon assumptions about future demand, market conditions and age. When we dispose of excess and obsolete inventories, the related disposals are charged against the inventory reserve. See Note 6 of Notes to Consolidated Financial Statements for additional information.

Property, Plant and Equipment

Property, Plant and Equipment

Property, plant and equipment, which is stated at cost, is depreciated using the straight-line method over the estimated useful lives of the assets. We depreciate building and land improvements from five to 39 years, office machinery and equipment from three to seven years, engineering machinery and equipment from three to seven years, and computer software from three to five years. Expenditures for repairs and maintenance are charged to expense as incurred. Betterments that materially prolong the lives of the assets are capitalized. Gains and losses on the disposal of property, plant and equipment are recorded in operating income. See Note 7 of Notes to Consolidated Financial Statements for additional information.

Liability for Warranty

Liability for Warranty

Our products generally include warranties of 90 days to five years for product defects. We accrue for warranty returns at the time revenue is recognized based on our estimate of the cost to repair or replace the defective products. We engage in extensive product quality programs and processes, including actively monitoring and evaluating the quality of our component suppliers. Our products continue to become more complex in both size and functionality as many of our product offerings migrate from line card applications to total systems. The increasing complexity of our products will cause warranty incidences, when they arise, to be more costly. Our estimates regarding future warranty obligations may change due to product failure rates, material usage, and other rework costs incurred in correcting a product failure. In addition, from time to time, specific warranty accruals may be recorded if unforeseen problems arise. Should our actual experience relative to these factors be worse than our estimates, we will be required to record additional warranty expense. Alternatively, if we provide for more reserves than we require, we will reverse a portion of such provisions in future periods. During 2016, we incurred an increase in warranty expense related to a product recall caused by a defect in a part provided by a third party supplier. The liability for warranty obligations totaled $8.5 million and $8.7 million at December 31, 2016 and 2015, respectively. These liabilities are included in accrued expenses in the accompanying consolidated balance sheets.

A summary of warranty expense and write-off activity for the years ended December 31, 2016, 2015 and 2014 is as follows:

Year Ended December 31,	2016			2015			2014
(In thousands)
Balance at beginning of period	$	8,739		$	8,415		$	8,977
Plus: Amounts charged to cost and expenses		8,561			2,998			3,103
Less: Deductions		(8,752	)		(2,674	)		(3,665	)
Balance at end of period	$	8,548		$	8,739		$	8,415

Pension Benefit Plan Obligations

Pension Benefit Plan Obligations

We maintain a defined benefit pension plan covering employees in certain foreign countries. Pension benefit plan obligations are based on various assumptions used by our actuaries in calculating these amounts. These assumptions include discount rates, compensation rate increases, expected return on plan assets, retirement rates and mortality rates. Actual results that differ from the assumptions and changes in assumptions could affect future expenses and obligations.

Stock-Based Compensation

Stock-Based Compensation

We have two Board and stockholder approved stock incentive plans from which stock options and other awards are available for grant to employees and directors. All employee and director stock options granted under our stock option plans have an exercise price equal to the fair market value of the award, as defined in the plan, of the underlying common stock on the grant date. There are currently no vesting provisions tied to performance or market conditions for any stock awards. Vesting for all outstanding award grants is based only on continued service as an employee or director of ADTRAN. All of our outstanding stock option awards are classified as equity awards.

Under the provisions of our approved plans, we made grants of performance stock units to certain of our executive officers in 2016, 2015, and 2014. The performance stock units are subject to a market condition based on the relative total shareholder return of ADTRAN against all the companies in the NASDAQ Telecommunications Index and vest at the end of a three-year performance period. The performance stock units are converted into shares of common stock upon vesting. Depending on the relative total shareholder return over the performance period, the executive officers may earn from 0% to 150% of the number of restricted stock units granted. The fair value of the award is based on the market price of our common stock on the date of grant, adjusted for the expected outcome of the impact of market conditions using a Monte Carlo Simulation valuation method. The recipients of the performance stock units also earn dividend credits during the performance period, which are paid in cash upon the issuance of common stock for the restricted stock units.

Stock-based compensation expense recognized in 2016, 2015 and 2014 was approximately $6.7 million, $6.7 million and $8.6 million, respectively. As of December 31, 2016, total compensation cost related to non-vested stock options, restricted stock units, performance stock units and restricted stock not yet recognized was approximately $16.4 million, which is expected to be recognized over an average remaining recognition period of 2.9 years. See Note 3 of Notes to Consolidated Financial Statements for additional information.

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets

We review long-lived assets used in operations for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable and the undiscounted cash flows estimated to be generated by the asset are less than the asset’s carrying value. An impairment loss would be recognized in the amount by which the recorded value of the asset exceeds the fair value of the asset, measured by the quoted market price of an asset or an estimate based on the best information available in the circumstances. There were no impairment losses recognized during 2016, 2015 or 2014.

Goodwill and Purchased Intangible Assets

Goodwill and Purchased Intangible Assets

We evaluate the carrying value of goodwill during the fourth quarter of each year and between annual evaluations if events occur or circumstances change that would more likely than not reduce the fair value of the reporting unit below its carrying amount. We have elected to first assess the qualitative factors to determine whether it is more likely than not that the fair value of the reporting unit to which the goodwill is assigned is less than its carrying amount as a basis for determining whether it is necessary to perform the two-step impairment test. If we determine that it is more likely than not that its fair value is less than its carrying amount, then the two-step impairment test will be performed. Based on the results of our qualitative assessment in 2016, we concluded that it was not necessary to perform the two-step impairment test. There have been no impairment losses recognized since the acquisition in 2011. Purchased intangible assets with finite lives are carried at cost, less accumulated amortization. Amortization is recorded over the estimated useful lives of the respective assets, which is 9 months to 14 years.

Research and Development Costs

Research and Development Costs

Research and development costs include compensation for engineers and support personnel, outside contracted services, depreciation and material costs associated with new product development, the enhancement of current products, and product cost reductions. We continually evaluate new product opportunities and engage in intensive research and product development efforts. Research and development costs totaled $124.8 million, $129.9 million and $132.3 million for the years ended December 31, 2016, 2015 and 2014, respectively.

Other Comprehensive Income

Other Comprehensive Income

Other comprehensive income consists of unrealized gains (losses) on available-for-sale securities, reclassification adjustments for amounts included in net income related to impairments of available-for-sale securities and realized gains (losses) on available-for-sale securities, defined benefit plan adjustments and foreign currency translation adjustments.

The following table presents changes in accumulated other comprehensive income, net of tax, by component for the years ended December 31, 2014, 2015 and 2016:

(In thousands)	Unrealized Gains (Losses) on Available- for-Sale Securities			Defined Benefit Plan Adjustments			Foreign Currency Adjustments			Total
Balance at December 31, 2013	$	10,737		$	(891	)	$	907		$	10,753
Other comprehensive income (loss) before    reclassifications		2,363			(4,866	)		(4,189	)		(6,692	)
Amounts reclassified from accumulated other    comprehensive income		(4,136	)		—			—			(4,136	)
Balance at December 31, 2014		8,964			(5,757	)		(3,282	)		(75	)
Other comprehensive income (loss) before    reclassifications		(844	)		1,589			(3,724	)		(2,979	)
Amounts reclassified from accumulated other    comprehensive income		(6,188	)		273			—			(5,915	)
Balance at December 31, 2015		1,932			(3,895	)		(7,006	)		(8,969	)
Other comprehensive income (loss) before    reclassifications		1,515			(1,229	)		(569	)		(283	)
Amounts reclassified from accumulated other    comprehensive income		(3,043	)		107			—			(2,936	)
Balance at December 31, 2016	$	404		$	(5,017	)	$	(7,575	)	$	(12,188	)

The following tables present the details of reclassifications out of accumulated other comprehensive income for the years ended December 31, 2016, 2015 and 2014:

(In thousands)	2016
Details about Accumulated Other Comprehensive Income Components	Amount Reclassified from Accumulated Other Comprehensive Income			Affected Line Item in the Statement Where Net Income Is Presented
Unrealized gains (losses) on available-for-sale securities:
Net realized gain on sales of securities	$	5,408		Net realized investment gain
Impairment expense		(419	)	Net realized investment gain
Defined benefit plan adjustments – actuarial losses		(156	)	(1)
Total reclassifications for the period, before tax		4,833
Tax (expense) benefit		(1,897	)
Total reclassifications for the period, net of tax	$	2,936

⁽¹⁾ Included in the computation of net periodic pension cost. See Note 11 of Notes to Consolidated Financial Statements.

(In thousands)	2015
Details about Accumulated Other Comprehensive Income Components	Amount Reclassified from Accumulated Other Comprehensive Income			Affected Line Item in the Statement Where Net Income Is Presented
Unrealized gains (losses) on available-for-sale securities:
Net realized gain on sales of securities	$	10,348		Net realized investment gain
Impairment expense		(203	)	Net realized investment gain
Defined benefit plan adjustments – actuarial losses		(396	)	(1)
Total reclassifications for the period, before tax		9,749
Tax (expense) benefit		(3,834	)
Total reclassifications for the period, net of tax	$	5,915

⁽¹⁾ Included in the computation of net periodic pension cost. See Note 11 of Notes to Consolidated Financial Statements.

(In thousands)	2014
Details about Accumulated Other Comprehensive Income Components	Amount Reclassified from Accumulated Other Comprehensive Income			Affected Line Item in the Statement Where Net Income Is Presented
Unrealized gains (losses) on available-for-sale securities:
Net realized gain on sales of securities	$	6,895		Net realized investment gain
Impairment expense		(115	)	Net realized investment gain
Total reclassifications for the period, before tax		6,780
Tax (expense) benefit		(2,644	)
Total reclassifications for the period, net of tax	$	4,136

The following tables present the tax effects related to the change in each component of other comprehensive income for the years ended December 31, 2016, 2015 and 2014:

	2016
(In thousands)	Before-Tax Amount			Tax (Expense) Benefit			Net-of-Tax Amount
Unrealized gains (losses) on available-for-sale securities	$	2,484		$	(969	)	$	1,515
Reclassification adjustment for amounts related to available-for-sale investments included in net income		(4,989	)		1,946			(3,043	)
Defined benefit plan adjustments		(1,782	)		553			(1,229	)
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income		156			(49	)		107
Foreign currency translation adjustment		(569	)		—			(569	)
Total Other Comprehensive Income (Loss)	$	(4,700	)	$	1,481		$	(3,219	)

	2015
(In thousands)	Before-Tax Amount			Tax (Expense) Benefit			Net-of-Tax Amount
Unrealized gains (losses) on available-for-sale securities	$	(1,384	)	$	540		$	(844	)
Reclassification adjustment for amounts related to available-    for-sale investments included in net income		(10,145	)		3,957			(6,188	)
Defined benefit plan adjustments		2,303			(714	)		1,589
Reclassification adjustment for amounts related to defined    benefit plan adjustments included in net income		396			(123	)		273
Foreign currency translation adjustment		(3,724	)		—			(3,724	)
Total Other Comprehensive Income (Loss)	$	(12,554	)	$	3,660		$	(8,894	)

	2014
(In thousands)	Before-Tax Amount			Tax (Expense) Benefit			Net-of-Tax Amount
Unrealized gains (losses) on available-for-sale securities	$	3,874		$	(1,511	)	$	2,363
Reclassification adjustment for amounts related to available-    for-sale investments included in net income		(6,780	)		2,644			(4,136	)
Defined benefit plan adjustments		(7,052	)		2,186			(4,866	)
Foreign currency translation adjustment		(4,189	)		—			(4,189	)
Total Other Comprehensive Income (Loss)	$	(14,147	)	$	3,319		$	(10,828	)

Income Taxes

Income Taxes

The provision for income taxes has been determined using the asset and liability approach of accounting for income taxes. Under this approach, deferred taxes represent the future tax consequences expected to occur when the reported amounts of assets and liabilities are recovered or paid. The provision for income taxes represents income taxes paid or payable for the current year plus the change in deferred taxes during the year. Deferred taxes result from the difference between financial and tax bases of our assets and liabilities and are adjusted for changes in tax rates and tax laws when such changes are enacted. Valuation allowances are recorded to reduce deferred tax assets when it is more likely than not that a tax benefit will not be realized.

We establish reserves to remove some or all of the tax benefit of any of our tax positions at the time we determine that the positions become uncertain.  We adjust these reserves, including any impact on the related interest and penalties, as facts and circumstances change.

Foreign Currency

Foreign Currency

We record transactions denominated in foreign currencies on a monthly basis using exchange rates from throughout the year. Assets and liabilities denominated in foreign currencies are translated at the balance sheet dates using the closing rates of exchange between those foreign currencies and the functional currency with any transaction gains or losses reported in other income (expense). Our primary exposures to foreign currency exchange rate movements are with our German subsidiary, whose functional currency is the Euro, our Australian subsidiary, whose functional currency is the Australian dollar, and our Mexican subsidiary, whose functional currency is the U.S. dollar. Adjustments resulting from translating financial statements of international subsidiaries are recorded as a component of accumulated other comprehensive income (loss).

Revenue Recognition

Revenue Recognition

Revenue is generally recognized when persuasive evidence of an arrangement exists, delivery has occurred, the product price is fixed or determinable, collection of the resulting receivable is reasonably assured, and product returns are reasonably estimable. For product sales, revenue is generally recognized upon shipment of the product to our customer in accordance with the title transfer terms of the sales agreement, generally Ex Works, per International Commercial Terms. In the case of consigned inventory, revenue is recognized when the end customer assumes ownership of the product. Contracts that contain multiple deliverables are evaluated to determine the units of accounting, and the consideration from the arrangement is allocated to each unit of accounting based on the relative selling price and corresponding terms of the contract. We use vendor-specific objective evidence of selling price. When this evidence is not available, we are generally not able to determine third-party evidence of selling price because of the extent of customization among competing products or services from other companies. In these instances, we use best estimates to allocate consideration to each respective unit of accounting. These estimates include analysis of respective bills of material and review and analysis of similar product and service offerings. We record revenue associated with installation services when respective contractual obligations are complete. In instances where customer acceptance is required, revenue is deferred until respective acceptance criteria have been met. Contracts that include both installation services and product sales are evaluated for revenue recognition in accordance with contract terms. As a result, installation services may be considered a separate deliverable or may be considered a combined single unit of accounting with the delivered product. Generally, either the purchaser, ADTRAN, or a third party can perform the installation of our products. Shipping fees are recorded as revenue and the related cost is included in cost of sales. Sales taxes invoiced to customers are included in revenues, and represent less than one percent of total revenues. The corresponding sales taxes paid are included in cost of goods sold. Value added taxes collected from customers in international jurisdictions are recorded in accrued expenses as a liability. Revenue is recorded net of discounts. Sales returns are recorded as a reduction of revenue and accrued based on historical sales return experience, which we believe provides a reasonable estimate of future returns.

A portion of our products are sold to a non-exclusive distribution network of major technology distributors in the United States. These large organizations then distribute or provide fulfillment services to an extensive network of VARs and SIs. VARs and SIs may be affiliated with us as a channel partner, or they may purchase from the distributor in an unaffiliated fashion. Additionally, with certain limitations our distributors may return unused and unopened product for stock-balancing purposes when such returns are accompanied by offsetting orders for products of equal or greater value.

We participate in cooperative advertising and market development programs with certain customers. We use these programs to reimburse customers for certain forms of advertising, and in general, to allow our customers credits up to a specified percentage of their net purchases. Our costs associated with these programs are estimated and included in marketing expenses in our consolidated statements of income. We also participate in rebate programs to provide sales incentives for certain products. Our costs associated with these programs are estimated and accrued at the time of sale, and are recorded as a reduction of sales in our consolidated statements of income.

Unearned Revenue

Unearned Revenue

Unearned revenue primarily represents customer billings on our maintenance service programs and unearned revenues relating to multiple element contracts where we still have contractual obligations to our customers. We currently offer maintenance contracts ranging from one to five years. Revenue attributable to maintenance contracts is recognized on a straight-line basis over the related contract term. In addition, we provide software maintenance and a variety of hardware maintenance services to customers under contracts with terms up to ten years. When we defer revenue related to multiple-element contracts where we still have contractual obligations, we also defer the related costs. Deferred costs are included in prepaid expenses and other assets and totaled $10.7 million and $5.2 million at December 31, 2016 and 2015, respectively.

Other Income (Expense), Net

Other Income (Expense), Net

Other income (expense), net, is comprised primarily of miscellaneous income and expense, gains and losses on foreign currency transactions, and investment account management fees. For the year ended December 31, 2014, other income (expense), net included a $2.4 million gain related to the settlement of working capital items from an acquisition transaction that closed in 2012.

Earnings Per Share

Earnings per Share

Earnings per common share, and earnings per common share assuming dilution, are based on the weighted average number of common shares and, when dilutive, common equivalent shares outstanding during the year. See Note 14 of Notes to Consolidated Financial Statements for additional information.

Dividends

Dividends

During 2016, 2015 and 2014, we paid shareholder dividends totaling $17.6 million, $18.4 million and $19.9 million, respectively. The Board of Directors presently anticipates that it will declare a regular quarterly dividend so long as the present tax treatment of dividends exists and adequate levels of liquidity are maintained. The following table shows dividends paid to our shareholders in each quarter of 2016, 2015 and 2014.

Dividends per Common Share
	2016		2015		2014
First Quarter	$	0.09	$	0.09	$	0.09
Second Quarter	$	0.09	$	0.09	$	0.09
Third Quarter	$	0.09	$	0.09	$	0.09
Fourth Quarter	$	0.09	$	0.09	$	0.09

On January 17, 2017, the Board of Directors declared a quarterly cash dividend of $0.09 per common share to be paid to shareholders of record at the close of business on February 2, 2017. The ex-dividend date was January 31, 2017 and the payment date was February 16, 2017. The quarterly dividend payment was $4.4 million.

Business Combinations

Business Combinations

We use the acquisition method to account for business combinations. Under the acquisition method of accounting, we recognize the assets acquired and liabilities assumed at their fair value on the acquisition date. Goodwill is measured as the excess of the consideration transferred over the net assets acquired. Costs incurred to complete the business combination, such as legal, accounting or other professional fees, are charged to general and administrative expenses as they are incurred.

Recently Issued Accounting Standards

Recently Issued Accounting Standards

In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) (ASU 2014-09), which supersedes the revenue recognition requirements in Topic 605, Revenue Recognition, including most industry-specific revenue recognition guidance throughout the Industry Topics of the Codification. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. In August 2015, the FASB issued ASU 2015-14, which deferred the effective date of ASU 2014-09 to fiscal years beginning after December 31, 2017, and interim periods within those fiscal years, with early adoption permitted for reporting periods beginning after December 15, 2016. Subsequently, the FASB issued ASUs in 2016 containing implementation guidance related to ASU 2014-09, including: ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net),which isintended to improve the operability and understandability of the implementation guidance on principal versus agent considerations; ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing,which is intended to clarify two aspects of Topic 606: identifying performance obligations and the licensing implementation guidance; ASU 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients,which contains certain provisions and practical expedients in response to identified implementation issues; and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, which is intended to clarify the Codification or to correct unintended application of guidance. ASU 2014-09 allows for either full retrospective or modified retrospective adoption. We plan to adopt ASU 2014-09 and the related ASUs on January 1, 2018, and we are currently evaluating the transition method that will be elected. We are continuing to evaluate the potential impact of these ASUs, and we believe the most significant potential impact relates to our accounting for software license and installation services revenues. We do not believe there will be a significant impact to product or maintenance revenues.

In July 2015, the FASB issued Accounting Standards Update No.  2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory (ASU 2015-11). Currently, Topic 330, Inventory, requires an entity to measure inventory at the lower of cost or market. Market could be replacement cost, net realizable value, or net realizable value less an approximately normal profit margin. ASU 2015-11 does not apply to inventory that is measured using last-in, first-out (LIFO) or the retail inventory method. The amendments apply to all other inventory, which includes inventory that is measured using first-in, first-out (FIFO) or average cost. ASU 2015-11 requires an entity to measure in scope inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. ASU 2015-11 is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. The amendments should be applied prospectively with earlier application permitted as of the beginning of an interim or annual reporting period. We adopted ASU 2015-05 in the first quarter of 2017, and there was no material impact on our financial position, results of operations and cash flows.

In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842) (ASU 2016-02). ASU 2016-02 requires an entity to recognize lease assets and lease liabilities on the balance sheet and to disclose key information about the entity's leasing arrangements. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. A modified retrospective approach is required. We anticipate the adoption of ASU 2016-02 will have a material impact on our financial position; however, we do not believe adoption will have a material impact on our results of operations. We believe the most significant impact relates to our accounting for operating leases for office space and equipment.

In March 2016, the FASB issued Accounting Standards Update No. 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting (ASU 2016-09). ASU 2016-09 simplifies several aspects of accounting for share-based compensation arrangements, including income tax effects, the classification of tax-related cash flows on the statement of cash flows, and accounting for forfeitures. ASU 2016-09 is effective for fiscal years beginning after December 15, 2016, including interim periods within those years. We adopted ASU 2016-09 in the first quarter of 2017, and there was no material impact on our financial position, results of operations and cash flows.

In January 2017, the FASB issued Accounting Standards Update No. 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04). ASU 2017-04 simplifies the measurement of goodwill by eliminating step 2 of the goodwill impairment test. Under ASU 2017-04, entities will be required to compare the fair value of a reporting unit to its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. ASU 2017-04 is effective for annual or interim impairment tests performed in fiscal years beginning after December 15, 2019, with early adoption permitted for annual or interim impairment tests performed on testing dates after January 1, 2017. The amendments should be applied prospectively. We do not expect the adoption of ASU 2017-04 will have a material impact on our financial position, results of operations or cash flows.

During 2016, we adopted the following accounting standards, which had no material effect on our financial position, results of operations or cash flows:

In April 2015, the FASB issued Accounting Standards Update No. 2015-05, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement (ASU 2015-05), which provides guidance on accounting for fees paid by a customer in a cloud computing arrangement. If a cloud computing arrangement includes a software license, then the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. ASU 2015-05 is effective for annual reporting periods beginning after December 15, 2015, including interim periods within that reporting period. The amendments may be applied either prospectively to all arrangements entered into or materially modified after the effective date or retrospectively. We adopted ASU 2015-05 during the first quarter of 2016 and will apply the new standard prospectively. The adoption of ASU 2015-05 did not have a material impact on our financial position, results of operations and cash flows.

In November 2015, the FASB issued Accounting Standards Update No. 2015-17, Balance Sheet Classification of Deferred Taxes (ASU 2015-17). ASU 2015-17 amends the existing guidance on income taxes to require the classification of all deferred tax assets and liabilities as non-current on the balance sheet. ASU 2015-17 is effective for fiscal years beginning after December 15, 2016, including interim periods within those years. Early adoption is permitted. The guidance may be applied either prospectively, for all deferred tax assets and liabilities, or retrospectively to all periods presented. We elected to early adopt ASU 2015-17 during the fourth quarter of 2016, and we applied the guidance retrospectively to all periods presented. As a result, $17.3 million and $18.9 million were reclassified from current deferred tax assets to non-current deferred tax assets at December 31, 2016 and 2015, respectively.

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Nature of Business and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Summary of Warranty Expense and Write-Off Activity

A summary of warranty expense and write-off activity for the years ended December 31, 2016, 2015 and 2014 is as follows:

Year Ended December 31,	2016			2015			2014
(In thousands)
Balance at beginning of period	$	8,739		$	8,415		$	8,977
Plus: Amounts charged to cost and expenses		8,561			2,998			3,103
Less: Deductions		(8,752	)		(2,674	)		(3,665	)
Balance at end of period	$	8,548		$	8,739		$	8,415

Changes in Accumulated Other Comprehensive Income, Net of Tax by Component

The following table presents changes in accumulated other comprehensive income, net of tax, by component for the years ended December 31, 2014, 2015 and 2016:

(In thousands)	Unrealized Gains (Losses) on Available- for-Sale Securities			Defined Benefit Plan Adjustments			Foreign Currency Adjustments			Total
Balance at December 31, 2013	$	10,737		$	(891	)	$	907		$	10,753
Other comprehensive income (loss) before    reclassifications		2,363			(4,866	)		(4,189	)		(6,692	)
Amounts reclassified from accumulated other    comprehensive income		(4,136	)		—			—			(4,136	)
Balance at December 31, 2014		8,964			(5,757	)		(3,282	)		(75	)
Other comprehensive income (loss) before    reclassifications		(844	)		1,589			(3,724	)		(2,979	)
Amounts reclassified from accumulated other    comprehensive income		(6,188	)		273			—			(5,915	)
Balance at December 31, 2015		1,932			(3,895	)		(7,006	)		(8,969	)
Other comprehensive income (loss) before    reclassifications		1,515			(1,229	)		(569	)		(283	)
Amounts reclassified from accumulated other    comprehensive income		(3,043	)		107			—			(2,936	)
Balance at December 31, 2016	$	404		$	(5,017	)	$	(7,575	)	$	(12,188	)

Reclassifications Out of Accumulated Other Comprehensive Income

The following tables present the details of reclassifications out of accumulated other comprehensive income for the years ended December 31, 2016, 2015 and 2014:

(In thousands)	2016
Details about Accumulated Other Comprehensive Income Components	Amount Reclassified from Accumulated Other Comprehensive Income			Affected Line Item in the Statement Where Net Income Is Presented
Unrealized gains (losses) on available-for-sale securities:
Net realized gain on sales of securities	$	5,408		Net realized investment gain
Impairment expense		(419	)	Net realized investment gain
Defined benefit plan adjustments – actuarial losses		(156	)	(1)
Total reclassifications for the period, before tax		4,833
Tax (expense) benefit		(1,897	)
Total reclassifications for the period, net of tax	$	2,936

⁽¹⁾ Included in the computation of net periodic pension cost. See Note 11 of Notes to Consolidated Financial Statements.

(In thousands)	2015
Details about Accumulated Other Comprehensive Income Components	Amount Reclassified from Accumulated Other Comprehensive Income			Affected Line Item in the Statement Where Net Income Is Presented
Unrealized gains (losses) on available-for-sale securities:
Net realized gain on sales of securities	$	10,348		Net realized investment gain
Impairment expense		(203	)	Net realized investment gain
Defined benefit plan adjustments – actuarial losses		(396	)	(1)
Total reclassifications for the period, before tax		9,749
Tax (expense) benefit		(3,834	)
Total reclassifications for the period, net of tax	$	5,915

⁽¹⁾ Included in the computation of net periodic pension cost. See Note 11 of Notes to Consolidated Financial Statements.

(In thousands)	2014
Details about Accumulated Other Comprehensive Income Components	Amount Reclassified from Accumulated Other Comprehensive Income			Affected Line Item in the Statement Where Net Income Is Presented
Unrealized gains (losses) on available-for-sale securities:
Net realized gain on sales of securities	$	6,895		Net realized investment gain
Impairment expense		(115	)	Net realized investment gain
Total reclassifications for the period, before tax		6,780
Tax (expense) benefit		(2,644	)
Total reclassifications for the period, net of tax	$	4,136

Other Comprehensive Income

The following tables present the tax effects related to the change in each component of other comprehensive income for the years ended December 31, 2016, 2015 and 2014:

	2016
(In thousands)	Before-Tax Amount			Tax (Expense) Benefit			Net-of-Tax Amount
Unrealized gains (losses) on available-for-sale securities	$	2,484		$	(969	)	$	1,515
Reclassification adjustment for amounts related to available-for-sale investments included in net income		(4,989	)		1,946			(3,043	)
Defined benefit plan adjustments		(1,782	)		553			(1,229	)
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income		156			(49	)		107
Foreign currency translation adjustment		(569	)		—			(569	)
Total Other Comprehensive Income (Loss)	$	(4,700	)	$	1,481		$	(3,219	)

	2015
(In thousands)	Before-Tax Amount			Tax (Expense) Benefit			Net-of-Tax Amount
Unrealized gains (losses) on available-for-sale securities	$	(1,384	)	$	540		$	(844	)
Reclassification adjustment for amounts related to available-    for-sale investments included in net income		(10,145	)		3,957			(6,188	)
Defined benefit plan adjustments		2,303			(714	)		1,589
Reclassification adjustment for amounts related to defined    benefit plan adjustments included in net income		396			(123	)		273
Foreign currency translation adjustment		(3,724	)		—			(3,724	)
Total Other Comprehensive Income (Loss)	$	(12,554	)	$	3,660		$	(8,894	)

	2014
(In thousands)	Before-Tax Amount			Tax (Expense) Benefit			Net-of-Tax Amount
Unrealized gains (losses) on available-for-sale securities	$	3,874		$	(1,511	)	$	2,363
Reclassification adjustment for amounts related to available-    for-sale investments included in net income		(6,780	)		2,644			(4,136	)
Defined benefit plan adjustments		(7,052	)		2,186			(4,866	)
Foreign currency translation adjustment		(4,189	)		—			(4,189	)
Total Other Comprehensive Income (Loss)	$	(14,147	)	$	3,319		$	(10,828	)

Summary of Dividends Paid Per Common Share

The following table shows dividends paid to our shareholders in each quarter of 2016, 2015 and 2014.

Dividends per Common Share
	2016		2015		2014
First Quarter	$	0.09	$	0.09	$	0.09
Second Quarter	$	0.09	$	0.09	$	0.09
Third Quarter	$	0.09	$	0.09	$	0.09
Fourth Quarter	$	0.09	$	0.09	$	0.09

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Business Combinations (Tables)

12 Months Ended

Dec. 31, 2016

Business Combinations [Abstract]

Allocation of the Purchase Price to the Estimated Fair Value of the Assets Acquired and Liabilities Assumed Subject to Working Capital Adjustments

The allocation of the purchase price to the estimated fair value of the assets acquired and liabilities assumed at the acquisition date, subject to working capital adjustments, is as follows:

(In Thousands)
Assets
Inventory	$	3,131
Property, plant and equipment		352
Intangible assets		4,700
Total assets acquired		8,183
Liabilities
Accounts payable		(1,250	)
Warranty payable		(61	)
Accrued wages and benefits		(122	)
Deferred income taxes		(2,265	)
Total liabilities assumed		(3,698	)
Total net assets		4,485
Gain on bargain purchase of a business, net of tax		(3,542	)
Total purchase price	$	943

Details of the Acquired Intangible Assets

The details of the acquired intangible assets are as follows:

In thousands	Value		Life (years)
Supply agreement	$	1,400		0.8
Customer relationships		1,200		6.0
Developed technology		800		10.0
License		500		1.3
Patent		500		7.3
Non-compete		200		2.3
Trade name		100		2.0
Total	$	4,700

Summary of Actual Revenue and Net Loss Included in Consolidated Statements of Income

The actual revenue and net loss included in our Consolidated Statements of Income for the period September 13, 2016 to December 31, 2016 are as follows:

(In thousands)	September 13 to December 31, 2016
Revenue	$	2,768
Net loss	$	(805	)

Summary of Supplemental Unaudited Pro Forma Information

The following supplemental unaudited pro forma information presents the financial results as if the acquisition had occurred on January 1, 2015. This supplemental unaudited pro forma information does not purport to be indicative of what would have occurred had the acquisition been completed on January 1, 2015, nor is it indicative of any future results. Aside from revising the 2015 net income for the effect of the bargain purchase gain, there were no material, non-recurring adjustments to this unaudited pro forma information.

(In thousands)	2016		2015
Pro forma revenue	$	641,170	$	603,923
Pro forma net income	$	31,212	$	22,945

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Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Stock-Based Compensation Expense Related to Stock Options, PSUs, Restricted Stock and RSUs

The following table summarizes stock-based compensation expense related to stock options, PSUs, restricted stock and RSUs for the years ended December 31, 2016, 2015 and 2014, which was recognized as follows:

(In thousands)	2016			2015			2014
Stock-based compensation expense included in cost of    sales	$	389		$	280		$	479
Selling, general and administrative expense		3,341			3,261			4,185
Research and development expense		2,965			3,171			3,899
Stock-based compensation expense included in operating    expenses		6,306			6,432			8,084
Total stock-based compensation expense		6,695			6,712			8,563
Tax benefit for expense associated with non-qualified    options		(963	)		(862	)		(1,157	)
Total stock-based compensation expense, net of tax	$	5,732		$	5,850		$	7,406

Summary of Stock Options Outstanding

The following table is a summary of our stock options outstanding as of December 31, 2015 and 2016 and the changes that occurred during 2016:

(In thousands, except per share amounts)	Number of Options			Weighted Average Exercise Price		Weighted Avg. Remaining Contractual Life in Years		Aggregate Intrinsic Value
Options outstanding, December 31, 2015		7,108		$	21.97		6.42	$	3,284
Options granted		19		$	18.24
Options exercised		(283	)	$	16.66
Options forfeited		(93	)	$	17.90
Options expired		(413	)	$	23.96
Options outstanding, December 31, 2016		6,338		$	22.14		5.63	$	16,972
Options vested and expected to vest, December 31, 2016		6,276		$	22.20		5.60	$	16,606
Options exercisable, December 31, 2016		4,757		$	23.67		4.73	$	9,137

Stock Options Outstanding

The following table further describes our stock options outstanding as of December 31, 2016:

	Options Outstanding						Options Exercisable
Range of Exercise Prices	Options Outstanding at 12/31/16 (In thousands)		Weighted Avg. Remaining Contractual Life in Years		Weighted Average Exercise Price		Options Exercisable at 12/31/16 (In thousands)		Weighted Average Exercise Price
$14.88 – 18.96		2,101		6.78	$	15.82		1,217	$	16.14
$18.97 – 23.45		1,380		5.79	$	20.17		881	$	20.84
$23.46 – 30.35		1,491		5.08	$	23.89		1,293	$	23.92
$30.36 – 41.92		1,366		4.29	$	31.94		1,366	$	31.94
		6,338						4,757

Summary of PSUs, Restricted Stock and RSUs Outstanding

The following table is a summary of our PSUs, restricted stock and RSUs outstanding as of December 31, 2015 and 2016 and the changes that occurred during 2016:

(In thousands, except per share amounts)	Number of shares			Weighted Average Grant Date Fair Value
Unvested PSUs, restricted stock and RSUs outstanding,    December 31, 2015		106		$	21.09
PSUs, restricted stock and RSUs granted		460		$	20.63
PSUs, restricted stock and RSUs vested		(46	)	$	22.50
PSUs, restricted stock and RSUs forfeited		(1	)	$	20.00
Unvested RSUs and restricted stock outstanding,    December 31, 2016		519		$	20.51

Stock Options [Member]

Summary of Weighted-Average Assumptions and Value of Options Granted

The weighted-average estimated fair value of stock options granted to employees during the years ended December 31, 2016, 2015 and 2014 was $5.22 per share, $4.28 per share and $6.31 per share, respectively, with the following weighted-average assumptions:

	2016			2015			2014
Expected volatility		34.79	%		34.57	%		39.05	%
Risk-free interest rate		1.36	%		1.81	%		1.79	%
Expected dividend yield		1.98	%		2.35	%		1.90	%
Expected life (in years)		6.25			6.23			6.33

Performance Stock Units (PSUs) [Member]

Summary of Weighted-Average Assumptions and Value of Options Granted

The PSU pricing model also requires the use of several significant assumptions that impact the fair value estimate. The estimated fair value of the PSUs granted to employees during the years ended December 31, 2016, 2015 and 2014 was $23.50 per share, $17.64 per share and $22.11 per share, respectively, with the following assumptions:

	2016			2015			2014
Expected volatility		29.79	%		31.34	%		36.40	%
Risk-free interest rate		1.17	%		1.20	%		0.96	%
Expected dividend yield		1.80	%		2.35	%		1.89	%

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Investments (Tables)

12 Months Ended

Dec. 31, 2016

Investments Debt And Equity Securities [Abstract]

Securities and Investments, Recorded at Either Fair Value or Cost

At December 31, 2016, we held the following securities and investments, recorded at either fair value or cost:

								Fair Value /
	Amortized		Gross Unrealized					Carrying
(In thousands)	Cost		Gains		Losses			Value
Deferred compensation plan assets	$	12,367	$	2,271	$	(42	)	$	14,596
Corporate bonds		66,522		64		(174	)		66,412
Municipal fixed-rate bonds		11,799		12		(37	)		11,774
Asset-backed bonds		10,201		19		(14	)		10,206
Mortgage/Agency-backed bonds		13,080		15		(91	)		13,004
U.S. government bonds		30,022		15		(270	)		29,767
Foreign government bonds		3,729		2		(1	)		3,730
Variable rate demand notes		11,855		—		—			11,855
Marketable equity securities		30,571		311		(1,503	)		29,379
Available-for-sale securities held at fair value	$	190,146	$	2,709	$	(2,132	)	$	190,723
Restricted investment held at cost									27,800
Other investments									767
Total carrying value of available-for-sale investments								$	219,290

At December 31, 2015, we held the following securities and investments, recorded at either fair value or cost:

								Fair Value /
	Amortized		Gross Unrealized					Carrying
(In thousands)	Cost		Gains		Losses			Value
Deferred compensation plan assets	$	11,325	$	1,575	$	(66	)	$	12,834
Corporate bonds		58,328		20		(734	)		57,614
Municipal fixed-rate bonds		26,414		28		(18	)		26,424
Asset-backed bonds		19,281		2		(44	)		19,239
Mortgage/Agency-backed bonds		15,463		1		(91	)		15,373
Government bonds		35,646		—		(248	)		35,398
Marketable equity securities		31,643		4,301		(1,693	)		34,251
Available-for-sale securities held at fair value	$	198,100	$	5,927	$	(2,894	)	$	201,133
Restricted investment held at cost									30,000
Other investments held at cost									1,289
Total carrying value of available-for-sale investments								$	232,422

Contractual Maturities of Corporate Bonds, Municipal Fixed-Rate Bonds, Asset-Backed Bonds, Mortgage/Agency-Backed Bonds, U.S. Government Bonds and Foreign Government Bonds

As of December 31, 2016, corporate bonds, municipal fixed-rate bonds, asset-backed bonds, mortgage/agency-backed bonds, U.S. government bonds, and foreign government bonds had the following contractual maturities:

(In thousands)	Corporate bonds		Municipal fixed-rate bonds		Asset-backed bonds		Mortgage / Agency-backed bonds		U.S. government bonds		Foreign government bonds
Less than one year	$	18,912	$	8,321	$	—	$	—	$	1,701	$	2,400
One to two years		32,497		1,703		635		976		4,903		1,330
Two to three years		11,486		351		2,415		980		13,072		—
Three to five years		3,517		1,399		5,402		—		10,091		—
Five to ten years		—		—		1,600		2,060		—		—
More than ten years		—		—		154		8,988		—		—
Total	$	66,412	$	11,774	$	10,206	$	13,004	$	29,767	$	3,730

Gross Realized Gains and Losses on Sale of Securities

The following table presents gross realized gains and losses related to our investments for the years ended December 31, 2016, 2015 and 2014:

Year Ended December 31, (In thousands)	2016			2015			2014
Gross realized gains	$	7,530		$	10,906		$	7,586
Gross realized losses	$	(1,607	)	$	(569	)	$	(308	)

Breakdown of Investments with Unrealized Losses

The following table presents the breakdown of investments with unrealized losses at December 31, 2016:

(In thousands)	Continuous Unrealized Loss Position for Less than 12 Months					Continuous Unrealized Loss Position for 12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Deferred compensation plan assets	$	294	$	(12	)	$	245	$	(30	)	$	539	$	(42	)
Corporate bonds		32,562		(166	)		2,722		(8	)		35,284		(174	)
Municipal fixed-rate bonds		8,936		(37	)		—		—			8,936		(37	)
Asset-backed bonds		2,986		(14	)		—		—			2,986		(14	)
Mortgage/Agency-backed bonds		7,842		(81	)		1,239		(10	)		9,081		(91	)
U.S. government bonds		26,449		(270	)		—		—			26,449		(270	)
Foreign government bonds		924		(1	)		—		—			924		(1	)
Marketable equity securities		21,607		(1,200	)		1,495		(303	)		23,102		(1,503	)
Total	$	101,600	$	(1,781	)	$	5,701	$	(351	)	$	107,301	$	(2,132	)

The following table presents the breakdown of investments with unrealized losses at December 31, 2015:

(In thousands)	Continuous Unrealized Loss Position for Less than 12 Months					Continuous Unrealized Loss Position for 12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Deferred compensation plan assets	$	1,243	$	(53	)	$	92	$	(13	)	$	1,335	$	(66	)
Corporate bonds		35,952		(566	)		3,042		(168	)		38,994		(734	)
Municipal fixed-rate bonds		9,160		(18	)		—		—			9,160		(18	)
Asset-backed bonds		16,857		(44	)		—		—			16,857		(44	)
Mortgage/Agency-backed bonds		15,216		(91	)		—		—			15,216		(91	)
Government bonds		35,397		(248	)		—		—			35,397		(248	)
Marketable equity securities		14,364		(1,564	)		374		(129	)		14,738		(1,693	)
Total	$	128,189	$	(2,584	)	$	3,508	$	(310	)	$	131,697	$	(2,894	)

Fair Value Measurements of Cash Equivalents Held in Money Market Funds and Investments

We have categorized our cash equivalents and our investments held at fair value into a three-level fair value hierarchy based on the priority of the inputs to the valuation technique for the cash equivalents and investments as follows: Level 1 - Values based on unadjusted quoted prices for identical assets or liabilities in an active market; Level 2 - Values based on quoted prices in markets that are not active or model inputs that are observable either directly or indirectly; Level 3 - Values based on prices or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs could include information supplied by investees.

	Fair Value Measurements at December 31, 2016 Using
(In thousands)	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	6,878	$	6,878	$	—	$	—
Commercial paper		17,222		—		17,222		—
Cash equivalents		24,100		6,878		17,222		—
Available-for-sale securities
Deferred compensation plan assets		14,596		14,596		—		—
Available-for-sale debt securities
Corporate bonds		66,412		—		66,412		—
Municipal fixed-rate bonds		11,774		—		11,774		—
Asset-backed bonds		10,206		—		10,206		—
Mortgage/Agency-backed bonds		13,004		—		13,004		—
U.S. government bonds		29,767		29,767		—		—
Foreign government bonds		3,730		—		3,730		—
Variable rate demand notes		11,855		—		11,855		—
Available-for-sale marketable equity securities
Marketable equity securities – technology industry		3,374		3,374		—		—
Marketable equity securities – other		26,005		26,005		—		—
Available-for-sale securities		190,723		73,742		116,981		—
Total	$	214,823	$	80,620	$	134,203	$	—
	Fair Value Measurements at December 31, 2015 Using
(In thousands)	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash equivalents
Money market funds	$	1,271	$	1,271	$	—	$	—
Commercial paper		11,696		—		11,696		—
Cash equivalents		12,967		1,271		11,696		—
Available-for-sale securities
Deferred compensation plan assets		12,834		12,834		—		—
Available-for-sale debt securities
Corporate bonds		57,614		—		57,614		—
Municipal fixed-rate bonds		26,424		—		26,424		—
Asset-backed bonds		19,239		—		19,239		—
Mortgage/Agency-backed bonds		15,373		—		15,373		—
Government bonds		35,398		35,398		—		—
Available-for-sale marketable equity securities
Marketable equity securities – technology industry		5,384		5,384		—		—
Marketable equity securities – other		28,867		28,867		—		—
Available-for-sale securities		201,133		82,483		118,650		—
Total	$	214,100	$	83,754	$	130,346	$	—

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Derivative Instruments and Hedging Activities (Tables)

12 Months Ended

Dec. 31, 2016

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Schedule of Fair Values of Hedging Instruments Recorded in Consolidated Balance Sheet

The fair values of our derivative instruments recorded in the Consolidated Balance Sheet as of December 31, 2016 and 2015 were as follows:

(In thousands)	Balance Sheet Location	2016		2015
Derivatives Not Designated as Hedging Instruments (Level 2):
Foreign exchange contracts – asset derivatives	Other receivables	$	159	$	—

Schedule of Change in Fair Values of Derivative Instruments Recorded in Consolidated Statements of Income

The change in the fair values of our derivative instruments recorded in the Consolidated Statements of Income during the years ended December 31, 2016, 2015 and 2014 were as follows:

(In thousands)	Income Statement Location	2016		2015		2014
Derivatives Not Designated as Hedging Instruments:
Foreign exchange contracts	Other income (expense)	$	724	$	511	$	1,852

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Inventory (Tables)

12 Months Ended

Dec. 31, 2016

Inventory Disclosure [Abstract]

Components of Inventory

At December 31, 2016 and 2015, inventory was comprised of the following:

(In thousands)	2016		2015
Raw materials	$	40,461	$	34,223
Work in process		4,003		2,893
Finished goods		60,653		54,417
Total Inventory, net	$	105,117	$	91,533

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Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2016

Property Plant And Equipment [Abstract]

Property, Plant and Equipment

At December 31, 2016 and 2015, property, plant and equipment were comprised of the following:

(In thousands)	2016			2015
Land	$	4,575		$	4,575
Building and land improvements		29,229			25,667
Building		68,301			68,301
Furniture and fixtures		18,477			17,347
Computer hardware and software		87,655			76,389
Engineering and other equipment		118,746			112,132
Total Property, Plant and Equipment		326,983			304,411
Less accumulated depreciation		(242,514	)		(231,178	)
Total Property, Plant and Equipment, net	$	84,469		$	73,233

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Goodwill and Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2016

Goodwill And Intangible Assets Disclosure [Abstract]

Summary of Intangible Assets

The following table presents our intangible assets as of December 31, 2016 and 2015:

(In thousands)	2016							2015
	Gross Value		Accumulated Amortization			Net Value		Gross Value		Accumulated Amortization			Net Value
Customer relationships	$	6,899	$	(3,208	)	$	3,691	$	5,828	$	(2,627	)	$	3,201
Developed technology		6,444		(5,061	)		1,383		5,720		(4,329	)		1,391
Intellectual property		2,340		(2,129	)		211		2,340		(1,854	)		486
Supply agreement		1,400		(544	)		856		—		—			—
License		500		(113	)		387		—		—			—
Patent		500		(20	)		480		—		—			—
Trade names		370		(285	)		85		270		(265	)		5
Non-compete		200		(26	)		174		11		(11	)		—
Total	$	18,653	$	(11,386	)	$	7,267	$	14,169	$	(9,086	)	$	5,083

Estimated Future Amortization Expense Related to Intangible Assets

As of December 31, 2016, the estimated future amortization expense of intangible assets is as follows:

(In thousands)	Amount
2017	$	2,867
2018		1,168
2019		655
2020		621
2021		568
Thereafter		1,388
Total	$	7,267

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Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Summary of Components of Provision for Income Taxes

A summary of the components of the provision for income taxes for the years ended December 31, 2016, 2015 and 2014 is as follows:

(In thousands)	2016			2015			2014
Current
Federal	$	12,733		$	7,504		$	7,626
State		1,141			279			599
International		477			(29	)		12,587
Total Current		14,351			7,754			20,812
Deferred
Federal		647			(585	)		(1,083	)
State		73			(66	)		(123	)
International		(3,405	)		(41	)		(4,320	)
Total Deferred		(2,685	)		(692	)		(5,526	)
Total Provision for Income Taxes	$	11,666		$	7,062		$	15,286

Effective Income Tax Rate Differs from Federal Statutory Rate

Our effective income tax rate differs from the federal statutory rate due to the following:

	2016			2015			2014
Tax provision computed at the federal statutory rate		35.00	%		35.00	%		35.00	%
State income tax provision, net of federal benefit		3.93			4.86			2.69
Federal research credits		(8.15	)		(12.55	)		(4.05	)
Foreign taxes		(0.34	)		2.10			(7.26	)
Tax-exempt income		(0.53	)		(1.94	)		(1.25	)
State tax incentives		(2.77	)		(5.04	)		(2.21	)
Stock-based compensation		2.53			6.91			3.06
Domestic production activity deduction		(2.23	)		(3.17	)		(1.15	)
Bargain purchase		(2.64	)		—			—
Other, net		0.08			1.30			0.69
Effective Tax Rate		24.88	%		27.47	%		25.52	%

Income Before Provision for Income Taxes

Income before provision for income taxes for the years ended December 31, 2016, 2015 and 2014 is as follows:

(In thousands)	2016			2015			2014
U.S. entities	$	54,077		$	27,400		$	23,812
International entities		(7,182	)		(1,692	)		36,094
Total	$	46,895		$	25,708		$	59,906

Principal Components of Current and Non-current Deferred Taxes

Deferred income taxes on the balance sheet result from temporary differences between the amount of assets and liabilities recognized for financial reporting and tax purposes. The principal components of our current and non-current deferred taxes are as follows:

(In thousands)	2016			2015
Deferred tax assets
Accounts receivable	$	—		$	7
Inventory		12,020			12,558
Accrued expenses		5,551			6,359
Investments		1,062			—
Deferred compensation		5,751			5,072
Stock-based compensation		4,724			4,704
Uncertain tax positions related to state taxes and related interest		762			1,026
Pensions		4,273			5,729
Foreign losses		6,486			5,389
State losses and credit carry-forwards		4,021			4,187
Federal loss and research carry-forwards		5,886			5,886
Valuation allowance		(6,149	)		(7,250	)
Total Deferred Tax Assets		44,387			43,667
Deferred tax liabilities
Property, plant and equipment		(4,433	)		(3,315	)
Accrued expenses		—			(2,791	)
Intellectual property		(1,918	)		(476	)
Investments		—			(70	)
Total Deferred Tax Liabilities		(6,351	)		(6,652	)
Net Deferred Tax Assets	$	38,036		$	37,015

Change in Unrecognized Income Tax Benefits

The change in the unrecognized income tax benefits for the years ended December 31, 2016, 2015 and 2014 is reconciled below:

(In thousands)	2016			2015			2014
Balance at beginning of period	$	2,537		$	3,334		$	3,240
Increases for tax position related to:
Prior years		95			—			—
Current year		428			280			522
Decreases for tax positions related to:
Prior years		—			(29	)		—
Settlements with taxing authorities		—			(103	)		—
Expiration of applicable statute of limitations		(834	)		(945	)		(428	)
Balance at end of period	$	2,226		$	2,537		$	3,334

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Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2016

Compensation And Retirement Disclosure [Abstract]

Schedule of Pension Benefit Plan Obligations and Funded Status

The pension benefit plan obligations and funded status at December 31, 2016 and 2015, are as follows:

(In thousands)	2016			2015
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	$	(26,851	)	$	(30,507	)
Service cost		(1,211	)		(1,314	)
Interest cost		(720	)		(615	)
Actuarial gain (loss) - experience		431			247
Actuarial gain (loss) - assumptions		(2,628	)		2,078
Benefit payments		52			81
Effects of foreign currency exchange rate changes		916			3,179
Projected benefit obligation at end of period		(30,011	)		(26,851	)
Change in plan assets:
Fair value of plan assets at beginning of period		19,213			20,338
Actual return on plan assets		1,494			988
Effects of foreign currency exchange rate changes		(662	)		(2,113	)
Fair value of plan assets at end of period		20,045			19,213
Funded (unfunded) status at end of period	$	(9,966	)	$	(7,638	)

Summary of Net Amounts Recognized Balance Sheet for the Unfunded Pension Liability

The net amounts recognized in the balance sheet for the unfunded pension liability as of December 31, 2016 and 2015 are as follows:

(In thousands)	2016			2015
Current liability	$	—		$	—
Non-current liability		(9,966	)		(7,638	)
Total	$	(9,966	)	$	(7,638	)

Components of Net Periodic Pension Cost and Amounts Recognized Other Comprehensive Income

The components of net periodic pension cost and amounts recognized in other comprehensive income for the years ended December 31, 2016, 2015 and 2014 are as follows:

(In thousands)	2016			2015			2014
Net periodic benefit cost:
Service cost	$	1,211		$	1,314		$	1,189
Interest cost		720			615			836
Expected return on plan assets		(1,057	)		(1,011	)		(1,086	)
Amortization of actuarial losses		175			407			—
Net periodic benefit cost		1,049			1,325			939
Other changes in plan assets and benefit obligations    recognized in other comprehensive income:
Net actuarial (gain) loss		1,782			(2,303	)		7,052
Amortization of actuarial losses		(156	)		(396	)		—
Amount recognized in other comprehensive income		1,626			(2,699	)		7,052
Total recognized in net periodic benefit cost and other    comprehensive income	$	2,675		$	(1,374	)	$	7,991

Accumulated Other Comprehensive Income

The amounts recognized in accumulated other comprehensive income as of December 31, 2016 and 2015 are as follows:

(In thousands)	2016		2015
Net actuarial loss	$	6,871	$	5,245

Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost

The weighted-average assumptions that were used to determine the net periodic benefit cost for the years ended December 31, 2016, 2015 and 2014 are as follows:

	2016			2015			2014
Discount rates		2.64	%		2.20	%		3.70	%
Rate of compensation increase		2.00	%		2.25	%		2.25	%
Expected long-term rates of return		5.40	%		5.40	%		5.40	%

Weighted-Average Assumptions Used to Determine Benefit Obligation

The weighted-average assumptions that were used to determine the benefit obligation at December 31, 2016 and 2015:

	2016			2015
Discount rates		1.90	%		2.64	%
Rate of compensation increase		2.00	%		2.25	%

Schedule of Pension Benefit Payments Expected Future Service

The following pension benefit payments, which reflect expected future service, as appropriate, are expected to be paid to participants:

(In thousands)
2017	$	348
2018		515
2019		699
2020		964
2021		1,079
2022 – 2026		5,156
Total	$	8,761

Schedule of Cash Equivalents and Investments Held at Fair Value

We have categorized our cash equivalents and our investments held at fair value into a three-level fair value hierarchy based on the priority of the inputs to the valuation technique for the cash equivalents and investments as follows: Level 1 - Values based on unadjusted quoted prices for identical assets or liabilities in an active market; Level 2 - Values based on quoted prices in markets that are not active or model inputs that are observable either directly or indirectly; Level 3 - Values based on prices or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs include information supplied by investees.

	Fair Value Measurements at December 31, 2016 Using
(In thousands)	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents	$	6	$	6	$	—	$	—
Available-for-sale securities
Bond funds:
Corporate bonds		12,546		12,546		—		—
Government bonds		2,037		2,037		—		—
Equity funds:
Large cap blend		4,462		4,462		—		—
Large cap value		249		249		—		—
Balanced fund		745		745		—		—
Available-for-sale securities		20,039		20,039		—		—
Total	$	20,045	$	20,045	$	—	$	—

	Fair Value Measurements at December 31, 2015 Using
(In thousands)	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents	$	3	$	3	$	—	$	—
Available-for-sale securities
Bond funds:
Corporate bonds		11,633		11,633		—		—
Government bonds		1,960		1,960		—		—
Equity funds:
Large cap blend		4,604		4,604		—		—
Large cap value		258		258		—		—
Balanced fund		755		755		—		—
Available-for-sale securities		19,210		19,210		—		—
Total	$	19,213	$	19,213	$	—	$	—

Fair Value of Assets Held by Trust and Amounts Payable to Plan Participants

The fair value of the assets held by the Trust and the amounts payable to the plan participants at December 31, 2016 and 2015 are as follows:

(In thousands)	2016		2015
Fair Value of Plan Assets
Long-term Investments	$	14,596	$	12,834
Total Fair Value of Plan Assets	$	14,596	$	12,834
Amounts Payable to Plan Participants
Non-current Liabilities	$	14,596	$	12,834
Total Amounts Payable to Plan Participants	$	14,596	$	12,834

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Segment Information and Major Customers (Tables)

12 Months Ended

Dec. 31, 2016

Segment Reporting [Abstract]

Sales and Gross Profit of Reportable Segments

The following table presents information about the reported sales and gross profit of our reportable segments for each of the years ended December 31, 2016, 2015 and 2014. Asset information by reportable segment is not reported, since we do not produce such information internally.

Sales and Gross Profit by Market Segment
(In thousands)	2016				2015				2014
	Sales		Gross Profit		Sales		Gross Profit		Sales		Gross Profit
Network Solutions	$	525,502	$	254,807	$	527,422	$	233,579	$	559,532	$	271,517
Services & Support		111,279		36,537		72,642		33,318		70,475		39,810
Total	$	636,781	$	291,344	$	600,064	$	266,897	$	630,007	$	311,327

Sales Information by Product Category

The table below presents sales information by product category for the years ended December 31, 2016, 2015 and 2014:

(In thousands)	2016		2015		2014
Access & Aggregation	$	436,372	$	405,698	$	401,769
Customer Devices		137,608		125,565		138,051
Traditional & Other Products		62,801		68,801		90,187
Total	$	636,781	$	600,064	$	630,007

Sales Information by Geographic Area

The following table presents sales information by geographic area for the years ended December 31, 2016, 2015 and 2014. International sales correlate to shipments with a non-U.S. destination.

(In thousands)	2016		2015		2014
United States	$	501,337	$	419,366	$	381,382
Germany		85,780		111,666		150,987
Other international		49,664		69,032		97,638
Total	$	636,781	$	600,064	$	630,007

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Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2016

Commitments And Contingencies Disclosure [Abstract]

Future Minimum Rental Payments under Non-Cancelable Operating Leases with Original Maturities of Greater than 12 Months

As of December 31, 2016, future minimum rental payments under non-cancelable operating leases with original maturities of greater than 12 months are as follows:

(In thousands)
2017	$	3,788
2018		2,043
2019		847
2020		741
Thereafter		3,243
Total	$	10,662

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Earnings per Share (Tables)

12 Months Ended

Dec. 31, 2016

Earnings Per Share [Abstract]

Summary of Calculation of Basic and Diluted Earnings Per Share

A summary of the calculation of basic and diluted earnings per share (EPS) for the years ended December 31, 2016, 2015 and 2014 is as follows:

(In thousands, except for per share amounts)	2016		2015		2014
Numerator
Net Income	$	35,229	$	18,646	$	44,620
Denominator
Weighted average number of shares – basic		48,724		51,145		55,120
Effect of dilutive securities:
Stock options		170		81		304
Restricted stock and restricted stock units		55		41		58
Weighted average number of shares – diluted	$	48,949	$	51,267	$	55,482
Net income per share – basic	$	0.72	$	0.36	$	0.81
Net income per share – diluted	$	0.72	$	0.36	$	0.80

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Summarized Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Quarterly Operating Results

The following table presents unaudited quarterly operating results for each of our last eight fiscal quarters. This information has been prepared on a basis consistent with our audited financial statements and includes all adjustments, consisting only of normal recurring adjustments, considered necessary for a fair presentation of the data.

Unaudited Quarterly Operating Results

(In thousands, except for per share amounts)

Three Months Ended	March 31, 2016		June 30, 2016		September 30, 2016		December 31, 2016
Net sales	$	142,204	$	162,701	$	168,890	$	162,986
Gross profit	$	65,794	$	78,955	$	75,808	$	70,787
Operating income	$	5,521	$	14,812	$	10,130	$	4,272
Net income	$	5,014	$	10,228	$	12,415	$	7,572
Earnings per common share	$	0.10	$	0.21	$	0.26	$	0.16
Earnings per common share assuming dilution (1)	$	0.10	$	0.21	$	0.26	$	0.16

Three Months Ended	March 31, 2015		June 30, 2015		September 30, 2015		December 31, 2015
Net sales	$	142,835	$	160,138	$	158,078	$	139,013
Gross profit	$	65,563	$	68,246	$	70,649	$	62,439
Operating income	$	1,963	$	644	$	8,072	$	2,800
Net income	$	3,317	$	2,544	$	7,067	$	5,718
Earnings per common share	$	0.06	$	0.05	$	0.14	$	0.12
Earnings per common share assuming dilution (1)	$	0.06	$	0.05	$	0.14	$	0.12

⁽¹⁾ Assumes exercise of dilutive stock options calculated under the treasury stock method.

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Nature of Business and Summary of Significant Accounting Policies - Additional Information (Detail)		12 Months Ended			65 Months Ended
	Jan. 17, 2017 $ / shares	Dec. 31, 2016 USD ($) Customer IncentivePlan	Dec. 31, 2015 USD ($) Customer	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) IncentivePlan	Feb. 16, 2017 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2008 USD ($)	Jan. 13, 1995 USD ($)
Summary of Significant Accounting Policy [Line Items]
Cash, uninsured amount		$ 77,900,000			$ 77,900,000
Bonds payable, carrying amount		27,800,000			27,800,000			$ 50,000,000	$ 20,000,000
Bonds payable, fair value		$ 28,100,000			28,100,000
Number of customers accounting for 63.3 and 37.3 percent of accounts receivable | Customer		3	3
Allowance for doubtful accounts			$ 19,000
Period of warranty for product defects		90 days to five years
Liability for warranty obligations		$ 8,548,000	8,739,000	$ 8,415,000	$ 8,548,000		$ 8,977,000
Number of stock incentive plans | IncentivePlan		2			2
Performance period		3 years
Stock-based compensation expense		$ 6,695,000	6,712,000	8,563,000
Total compensation cost related to non-vested stock options, restricted stock units, performance stock units and restricted stock not yet recognized		$ 16,400,000			$ 16,400,000
Recognition period of non-vested compensation cost		2 years 10 months 24 days
Impairment losses recognized on long-lived assets		$ 0	0	0
Impairment losses recognized on goodwill and other intangible assets					0
Research and development costs		$ 124,804,000	129,876,000	132,258,000
Percentage of sales taxes collected from customers		1.00%
Other income (expense) - Gain on previous acquisition of working capital		$ (651,000)	(1,465,000)	1,175,000
Dividend payments		$ 17,600,000	18,400,000	19,900,000
Dividend declaration date		Jan. 17, 2017
Dividend record date		Feb. 02, 2017
Dividend payment date		Feb. 16, 2017
Ex-dividend date		Jan. 31, 2017
Accounting Standards Update No. 2015-17 [Member]
Summary of Significant Accounting Policy [Line Items]
Non-current deferred tax assets		$ 17,300,000	18,900,000		17,300,000
Subsequent Events [Member]
Summary of Significant Accounting Policy [Line Items]
Common stock dividends per share declared | $ / shares	$ 0.09
Quarterly dividend payable subsequent to balance sheet date						$ 4,400,000
Nokia Siemens Networks [Member]
Summary of Significant Accounting Policy [Line Items]
Other income (expense) - Gain on previous acquisition of working capital				$ 2,400,000
Prepaid Expenses and Other Current Assets [Member]
Summary of Significant Accounting Policy [Line Items]
Deferred costs related to prepaid and other assets		$ 10,700,000	$ 5,200,000		$ 10,700,000
Minimum [Member]
Summary of Significant Accounting Policy [Line Items]
Amortization, estimated useful lives		9 months
Maintenance contract period		1 year
Minimum [Member] | Performance Stock Units (PSUs) [Member]
Summary of Significant Accounting Policy [Line Items]
Percentage of performance stock units granted		0.00%
Maximum [Member]
Summary of Significant Accounting Policy [Line Items]
Amortization, estimated useful lives		14 years
Maintenance contract period		5 years
Maximum [Member] | Performance Stock Units (PSUs) [Member]
Summary of Significant Accounting Policy [Line Items]
Percentage of performance stock units granted		150.00%
Building and Land Improvements [Member] | Minimum [Member]
Summary of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives		5 years
Building and Land Improvements [Member] | Maximum [Member]
Summary of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives		39 years
Office Machinery and Equipment [Member] | Minimum [Member]
Summary of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives		3 years
Office Machinery and Equipment [Member] | Maximum [Member]
Summary of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives		7 years
Engineering Machinery and Equipment [Member] | Minimum [Member]
Summary of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives		3 years
Engineering Machinery and Equipment [Member] | Maximum [Member]
Summary of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives		7 years
Computer Software [Member] | Minimum [Member]
Summary of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives		3 years
Computer Software [Member] | Maximum [Member]
Summary of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives		5 years
Credit Concentration Risk [Member]
Summary of Significant Accounting Policy [Line Items]
Percentage of accounts receivable accounted by each customers		63.30%	37.30%		63.30%

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Nature of Business and Summary of Significant Accounting Policies - Summary of Warranty Expense and Write-Off Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Balance at beginning of period	$ 8,739	$ 8,415	$ 8,977
Plus: Amounts charged to cost and expenses	8,561	2,998	3,103
Less: Deductions	(8,752)	(2,674)	(3,665)
Balance at end of period	$ 8,548	$ 8,739	$ 8,415

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Nature of Business and Summary of Significant Accounting Policies (Other Comprehensive Income) - Changes in Accumulated Other Comprehensive Income, Net of Tax by Component (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (8,969)	$ (75)	$ 10,753
Other comprehensive income (loss) before reclassifications	(283)	(2,979)	(6,692)
Amounts reclassified from accumulated other comprehensive income	(2,936)	(5,915)	(4,136)
Ending balance	(12,188)	(8,969)	(75)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,932	8,964	10,737
Other comprehensive income (loss) before reclassifications	1,515	(844)	2,363
Amounts reclassified from accumulated other comprehensive income	(3,043)	(6,188)	(4,136)
Ending balance	404	1,932	8,964
Defined Benefit Plan Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(3,895)	(5,757)	(891)
Other comprehensive income (loss) before reclassifications	(1,229)	1,589	(4,866)
Amounts reclassified from accumulated other comprehensive income	107	273
Ending balance	(5,017)	(3,895)	(5,757)
Foreign Currency Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(7,006)	(3,282)	907
Other comprehensive income (loss) before reclassifications	(569)	(3,724)	(4,189)
Ending balance	$ (7,575)	$ (7,006)	$ (3,282)

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Nature of Business and Summary of Significant Accounting Policies (Other Comprehensive Income) - Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Defined benefit plan adjustments – actuarial losses									$ (2,628)	$ 2,078
Income before provision for income taxes									46,895	25,708	$ 59,906
Tax (expense) benefit									(11,666)	(7,062)	(15,286)
Total reclassifications for the period, net of tax	$ 7,572	$ 12,415	$ 10,228	$ 5,014	$ 5,718	$ 7,067	$ 2,544	$ 3,317	35,229	18,646	44,620
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Defined benefit plan adjustments – actuarial losses									(156)	(396)
Income before provision for income taxes									4,833	9,749	6,780
Tax (expense) benefit									(1,897)	(3,834)	(2,644)
Total reclassifications for the period, net of tax									2,936	5,915	4,136
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net realized investment gain									5,408	10,348	6,895
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Impairment Expense [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Net realized investment gain									$ (419)	$ (203)	$ (115)

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Nature of Business and Summary of Significant Accounting Policies (Other Comprehensive Income) - Tax Effects Related to the Change in Each Component of Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Unrealized gains (losses) on available-for-sale securities, Before-Tax Amount	$ 2,484	$ (1,384)	$ 3,874
Unrealized gains (losses) on available-for-sale securities, Tax (Expense) Benefit	(969)	540	(1,511)
Unrealized gains (losses) on available-for-sale securities, Net-of-Tax Amount	1,515	(844)	2,363
Reclassification adjustment for amounts related to available-for-sale investments included in net income, Before-Tax Amount	(4,989)	(10,145)	(6,780)
Reclassification adjustment for amounts related to available-for-sale investments included in net income, Tax (Expense) Benefit	1,946	3,957	2,644
Reclassification adjustment for amounts related to available-for-sale investments included in net income, Net-of-Tax Amount	(3,043)	(6,188)	(4,136)
Defined benefit plan adjustments, Before-Tax Amount	(1,782)	2,303	(7,052)
Defined benefit plan adjustments, Tax (Expense) Benefit	553	(714)	2,186
Defined benefit plan adjustments, Net-of-Tax Amount	(1,229)	1,589	(4,866)
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income, Before-Tax Amount	156	396
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income, Tax (Expense) Benefit	(49)	(123)
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income, Net-of-Tax Amount	107	273
Foreign currency translation adjustment, Before-Tax Amount	(569)	(3,724)	(4,189)
Foreign currency translation adjustment, Net-of-Tax Amount	(569)	(3,724)	(4,189)
Total Other Comprehensive Income (Loss), Before-Tax Amount	(4,700)	(12,554)	(14,147)
Total Other Comprehensive Income (Loss), Tax (Expense) Benefit	1,481	3,660	3,319
Other Comprehensive Loss, net of tax	$ (3,219)	$ (8,894)	$ (10,828)

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Nature of Business and Summary of Significant Accounting Policies - Summary of Dividends Paid Per Common Share (Detail) - $ / shares	3 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Dividends [Abstract]
Dividends per Common Share	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09

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Business Combinations - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Sep. 13, 2016	Dec. 31, 2016
Business Acquisition [Line Items]
Cash consideration		$ 943
Bargain purchase gain net of income taxes		$ 3,542
CommScope, Inc. Subsidiaries Fiber Access Products, Technologies and Service Relationships [Member]
Business Acquisition [Line Items]
Date of acquisition		Sep. 13, 2016
Business acquisition, description		On September 13, 2016, we acquired key fiber access products, technologies and service relationships from subsidiaries of CommScope, Inc. for $0.9 million in cash. This acquisition will enhance our solutions for the cable MSO industry and will provide cable operators with the scalable solutions, services and support they require to compete in the multi-gigabit service delivery market.
Cash consideration	$ 943
Bargain purchase gain net of income taxes	$ 3,542
Acquisition and integration related expenses and amortization of acquired intangibles		$ 1,000

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Business Combinations - Allocation of the Purchase Price to the Estimated Fair Value of the Assets Acquired and Liabilities Assumed Subject to Working Capital Adjustments (Detail) - USD ($) $ in Thousands		12 Months Ended
	Sep. 13, 2016	Dec. 31, 2016
Liabilities
Gain on bargain purchase of a business, net of tax		$ (3,542)
Total purchase price		$ 943
CommScope, Inc. Subsidiaries Fiber Access Products, Technologies and Service Relationships [Member]
Assets
Inventory	$ 3,131
Property, plant and equipment	352
Intangible assets	4,700
Total assets acquired	8,183
Liabilities
Accounts payable	(1,250)
Warranty payable	(61)
Accrued wages and benefits	(122)
Deferred income taxes	(2,265)
Total liabilities assumed	(3,698)
Total net assets	4,485
Gain on bargain purchase of a business, net of tax	(3,542)
Total purchase price	$ 943

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Business Combinations - Details of the Acquired Intangible Assets (Detail) - CommScope, Inc. Subsidiaries Fiber Access Products, Technologies and Service Relationships [Member] $ in Thousands	Sep. 13, 2016 USD ($)
Business Acquisition [Line Items]
Total, Value	$ 4,700
Supply Agreement [Member]
Business Acquisition [Line Items]
Total, Value	$ 1,400
Life (years)	9 months 18 days
Customer Relationships [Member]
Business Acquisition [Line Items]
Total, Value	$ 1,200
Life (years)	6 years
Developed Technology [Member]
Business Acquisition [Line Items]
Total, Value	$ 800
Life (years)	10 years
License [Member]
Business Acquisition [Line Items]
Total, Value	$ 500
Life (years)	1 year 3 months 18 days
Patent [Member]
Business Acquisition [Line Items]
Total, Value	$ 500
Life (years)	7 years 3 months 18 days
Non-compete [Member]
Business Acquisition [Line Items]
Total, Value	$ 200
Life (years)	2 years 3 months 18 days
Trade Name [Member]
Business Acquisition [Line Items]
Total, Value	$ 100
Life (years)	2 years

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Business Combinations - Summary of Actual Revenue and Net Loss Included in Consolidated Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								4 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Revenue	$ 162,986	$ 168,890	$ 162,701	$ 142,204	$ 139,013	$ 158,078	$ 160,138	$ 142,835		$ 636,781	$ 600,064	$ 630,007
Net loss	$ 7,572	$ 12,415	$ 10,228	$ 5,014	$ 5,718	$ 7,067	$ 2,544	$ 3,317		$ 35,229	$ 18,646	$ 44,620
CommScope, Inc. Subsidiaries Fiber Access Products, Technologies and Service Relationships [Member]
Business Acquisition [Line Items]
Revenue									$ 2,768
Net loss									$ (805)

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Business Combinations - Summary of Supplemental Unaudited Pro Forma Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Business Combinations [Abstract]
Pro forma revenue	$ 641,170	$ 603,923
Pro forma net income	$ 31,212	$ 22,945

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Stock-Based Compensation (Stock Incentive Program Descriptions) - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Jan. 20, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term	10 years
Estimated forfeitures for stock options and RSUs	3.70%
PSUs and Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeiture rate for PSUs and restricted stock	0.00%
2006 Employee Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock authorized	13,000,000
Vesting period	4 years
Contractual term	10 years
2010 Directors Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock authorized	500,000
Contractual term	10 years
2015 Employee Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of common stock authorized		7,700,000
Vesting period	4 years
Contractual term	10 years
Multiplier used when issuing PSUs, restricted stock and RSUs		2.5
Minimum [Member] | 2006 Employee Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration date of options	2017
Minimum [Member] | 2010 Directors Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration date of options	2017
Minimum [Member] | 2015 Employee Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration date of options	2025
Maximum [Member] | 2006 Employee Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration date of options	2024
Maximum [Member] | 2010 Directors Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration date of options	2019
Maximum [Member] | 2015 Employee Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration date of options	2026

XML

Stock-Based Compensation - Stock-Based Compensation Expense Related to Stock Options, PSUs, Restricted Stock and RSUs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,695	$ 6,712	$ 8,563
Tax benefit for expense associated with non-qualified options	(963)	(862)	(1,157)
Total stock-based compensation expense, net of tax	5,732	5,850	7,406
Cost of Sales [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	389	280	479
Selling, General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	3,341	3,261	4,185
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	2,965	3,171	3,899
Operating Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,306	$ 6,432	$ 8,084

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Stock-Based Compensation - Summary of Stock Options Outstanding (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Options outstanding, Beginning Balance	7,108
Number of Options, Options granted	19
Number of Options, Options exercised	(283)	(60)	(147)
Number of Options, Options forfeited	(93)
Number of Options, Options expired	(413)
Number of Options, Options outstanding, Ending Balance	6,338	7,108
Number of Options, Options vested and expected to vest	6,276
Number of Options, Options exercisable	4,757
Weighted Average Exercise Price, Options outstanding, Beginning Balance	$ 21.97
Weighted Average Exercise Price, Options granted	18.24
Weighted Average Exercise Price, Options exercised	16.66
Weighted Average Exercise Price, Options forfeited	17.90
Weighted Average Exercise Price, Options expired	23.96
Weighted Average Exercise Price, Options outstanding, Ending Balance	22.14	$ 21.97
Weighted Average Exercise Price, Options vested and expected to vest	22.20
Weighted Average Exercise Price, Options exercisable	$ 23.67
Weighted Average Remaining Contractual Life In Years, Options outstanding	5 years 7 months 17 days	6 years 5 months 1 day
Weighted Average Remaining Contractual Life In Years, Options vested and expected to vest	5 years 7 months 6 days
Weighted Average Remaining Contractual Life In Years, Options exercisable	4 years 8 months 23 days
Aggregate Intrinsic Value, Options outstanding, Beginning Balance	$ 3,284
Aggregate Intrinsic Value, Options outstanding, Ending Balance	16,972	$ 3,284
Aggregate Intrinsic Value, Options vested and expected to vest	16,606
Aggregate Intrinsic Value, Options exercisable	$ 9,137

XML

Stock-Based Compensation (Stock Options) - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost related to non-vested stock options not yet recognized	$ 16.4
Recognition period of non-vested compensation cost	2 years 10 months 24 days
Share-based Compensation Arrangement by Share-based Payment Award, Options Outstanding, Weighted Average Exercise Price, and Additional Disclosures [Abstract]
Number of shares available for grant	5.6
Total pre-tax intrinsic value of options exercised	$ 1.1	$ 0.1	$ 0.7
Fair value of options fully vested	5.7	$ 6.6	$ 7.7
Non Vested Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost related to non-vested stock options not yet recognized	$ 7.5
Recognition period of non-vested compensation cost	2 years 1 month 6 days

XML

Stock-Based Compensation - Stock Options Outstanding (Detail) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding at 12/31/16	6,338	7,108
Options Exercisable at 12/31/16	4,757
Weighted Average Exercise Price, Options exercisable	$ 23.67
$14.88 - 18.96 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Lower Range Limit	14.88
Upper Range Limit	$ 18.96
Options Outstanding at 12/31/16	2,101
Weighted Avg. Remaining Contractual Life In Years, Options Outstanding	6 years 9 months 11 days
Weighted Average Exercise Price, Options Outstanding	$ 15.82
Options Exercisable at 12/31/16	1,217
Weighted Average Exercise Price, Options exercisable	$ 16.14
$18.97 - 23.45 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Lower Range Limit	18.97
Upper Range Limit	$ 23.45
Options Outstanding at 12/31/16	1,380
Weighted Avg. Remaining Contractual Life In Years, Options Outstanding	5 years 9 months 15 days
Weighted Average Exercise Price, Options Outstanding	$ 20.17
Options Exercisable at 12/31/16	881
Weighted Average Exercise Price, Options exercisable	$ 20.84
$23.46 - 30.35 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Lower Range Limit	23.46
Upper Range Limit	$ 30.35
Options Outstanding at 12/31/16	1,491
Weighted Avg. Remaining Contractual Life In Years, Options Outstanding	5 years 29 days
Weighted Average Exercise Price, Options Outstanding	$ 23.89
Options Exercisable at 12/31/16	1,293
Weighted Average Exercise Price, Options exercisable	$ 23.92
$30.36 - 41.92 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Lower Range Limit	30.36
Upper Range Limit	$ 41.92
Options Outstanding at 12/31/16	1,366
Weighted Avg. Remaining Contractual Life In Years, Options Outstanding	4 years 3 months 15 days
Weighted Average Exercise Price, Options Outstanding	$ 31.94
Options Exercisable at 12/31/16	1,366
Weighted Average Exercise Price, Options exercisable	$ 31.94

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Stock-Based Compensation (PSUs, Restricted Stock and RSUs) - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost related to non-vested stock options not yet recognized	$ 16.4
Recognition period of non-vested compensation cost	2 years 10 months 24 days
Performance Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Performance Stock Units (PSUs) [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance stock units granted	0.00%
Performance Stock Units (PSUs) [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance stock units granted	150.00%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
PSUs, Restricted Stock and RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost related to non-vested stock options not yet recognized	$ 8.9
Recognition period of non-vested compensation cost	3 years 7 months 6 days

XML

Stock-Based Compensation - Summary of PSUs, Restricted Stock and RSUs Outstanding (Detail) shares in Thousands	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Unvested PSUs, restricted stock and RSUs outstanding, beginning balance | shares	106
Number of PSUs, restricted stock and RSUs granted | shares	460
Number of PSUs, restricted stock and RSUs vested | shares	(46)
Number of PSUs, restricted stock and RSUs forfeited | shares	(1)
Number of Unvested RSUs and restricted stock outstanding, ending balance | shares	519
Weighted Average Grant Date Fair Value, Unvested PSUs, restricted stock and RSUs outstanding, Beginning balance | $ / shares	$ 21.09
Weighted Average Grant Date Fair Value, PSUs, restricted stock and RSUs granted | $ / shares	20.63
Weighted Average Grant Date Fair Value, PSUs, restricted stock and RSUs vested | $ / shares	22.50
Weighted Average Grant Date Fair Value, PSUs, restricted stock and RSUs forfeited | $ / shares	20.00
Weighted Average Grant Date Fair Value, Unvested RSUs and restricted stock outstanding, Ending balance | $ / shares	$ 20.51

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Stock-Based Compensation (Valuation and Expense Information) - Additional Information (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average estimated value	$ 5.22	$ 4.28	$ 6.31
Contractual term	10 years
Weighted average grant date fair value, PSUs granted	$ 20.63
Performance Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value, PSUs granted	$ 23.50	$ 17.64	$ 22.11

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Stock-Based Compensation - Summary of Weighted-Average Assumptions and Value of Options Granted (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	34.79%	34.57%	39.05%
Risk-free interest rate	1.36%	1.81%	1.79%
Expected dividend yield	1.98%	2.35%	1.90%
Expected life (in years)	6 years 3 months	6 years 2 months 23 days	6 years 3 months 29 days
Performance Stock Units (PSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	29.79%	31.34%	36.40%
Risk-free interest rate	1.17%	1.20%	0.96%
Expected dividend yield	1.80%	2.35%	1.89%

XML

Investments - Securities and Investments, Recorded at Either Fair Value or Cost (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 190,146	$ 198,100
Gross Unrealized Gains	2,709	5,927
Gross Unrealized Losses	(2,132)	(2,894)
Available-for-sale-securities, Fair Value/Carrying Value	190,723	201,133
Restricted investment held at cost	27,800	30,000
Other investments held at cost	767	1,289
Total carrying value of available-for-sale investments	219,290	232,422
Deferred Compensation Plan Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,367	11,325
Gross Unrealized Gains	2,271	1,575
Gross Unrealized Losses	(42)	(66)
Available-for-sale-securities, Fair Value/Carrying Value	14,596	12,834
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	66,522	58,328
Gross Unrealized Gains	64	20
Gross Unrealized Losses	(174)	(734)
Available-for-sale-securities, Fair Value/Carrying Value	66,412	57,614
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,799	26,414
Gross Unrealized Gains	12	28
Gross Unrealized Losses	(37)	(18)
Available-for-sale-securities, Fair Value/Carrying Value	11,774	26,424
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,201	19,281
Gross Unrealized Gains	19	2
Gross Unrealized Losses	(14)	(44)
Available-for-sale-securities, Fair Value/Carrying Value	10,206	19,239
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,080	15,463
Gross Unrealized Gains	15	1
Gross Unrealized Losses	(91)	(91)
Available-for-sale-securities, Fair Value/Carrying Value	13,004	15,373
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,022	35,646
Gross Unrealized Gains	15
Gross Unrealized Losses	(270)	(248)
Available-for-sale-securities, Fair Value/Carrying Value	29,767	35,398
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,729
Gross Unrealized Gains	2
Gross Unrealized Losses	(1)
Available-for-sale-securities, Fair Value/Carrying Value	3,730
Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,855
Available-for-sale-securities, Fair Value/Carrying Value	11,855
Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,571	31,643
Gross Unrealized Gains	311	4,301
Gross Unrealized Losses	(1,503)	(1,693)
Available-for-sale-securities, Fair Value/Carrying Value	$ 29,379	$ 34,251

XML

Investments - Contractual Maturities of Corporate Bonds, Municipal Fixed-Rate Bonds, Asset-Backed Bonds, Mortgage/Agency-Backed Bonds, U.S. Government Bonds and Foreign Government Bonds (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale-securities, Fair Value/Carrying Value	$ 190,723	$ 201,133
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	18,912
One to two years	32,497
Two to three years	11,486
Three to five years	3,517
Available-for-sale-securities, Fair Value/Carrying Value	66,412	57,614
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	8,321
One to two years	1,703
Two to three years	351
Three to five years	1,399
Available-for-sale-securities, Fair Value/Carrying Value	11,774	26,424
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	635
Two to three years	2,415
Three to five years	5,402
Five to ten years	1,600
More than ten years	154
Available-for-sale-securities, Fair Value/Carrying Value	10,206	19,239
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	976
Two to three years	980
Five to ten years	2,060
More than ten years	8,988
Available-for-sale-securities, Fair Value/Carrying Value	13,004	15,373
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	1,701
One to two years	4,903
Two to three years	13,072
Three to five years	10,091
Available-for-sale-securities, Fair Value/Carrying Value	29,767	$ 35,398
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	2,400
One to two years	1,330
Available-for-sale-securities, Fair Value/Carrying Value	$ 3,730

XML

Investments - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) Security	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Investments [Line Items]
Identification of potential other-than-temporary impairments	25.00%
Impairment of investments | $	$ 0.8	$ 0.2	$ 0.1
Number of marketable equity securities in an unrealized loss position | Security	293
Investment [Member] | Issuer Concentration [Member] | Market Value of Total Investment Portfolio [Member]
Schedule of Investments [Line Items]
Investment concentration risk percentage	5.00%

XML

Investments - Gross Realized Gains and Losses on Sale of Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments Debt And Equity Securities [Abstract]
Gross realized gains	$ 7,530	$ 10,906	$ 7,586
Gross realized losses	$ (1,607)	$ (569)	$ (308)

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Investments - Breakdown of Investments with Unrealized Losses (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	$ 101,600	$ 128,189
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(1,781)	(2,584)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value	5,701	3,508
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses	(351)	(310)
Total Fair Value	107,301	131,697
Total Unrealized Losses	(2,132)	(2,894)
Deferred Compensation Plan Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	294	1,243
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(12)	(53)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value	245	92
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses	(30)	(13)
Total Fair Value	539	1,335
Total Unrealized Losses	(42)	(66)
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	32,562	35,952
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(166)	(566)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value	2,722	3,042
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses	(8)	(168)
Total Fair Value	35,284	38,994
Total Unrealized Losses	(174)	(734)
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	8,936	9,160
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(37)	(18)
Total Fair Value	8,936	9,160
Total Unrealized Losses	(37)	(18)
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	2,986	16,857
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(14)	(44)
Total Fair Value	2,986	16,857
Total Unrealized Losses	(14)	(44)
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	7,842	15,216
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(81)	(91)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value	1,239
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses	(10)
Total Fair Value	9,081	15,216
Total Unrealized Losses	(91)	(91)
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	26,449	35,397
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(270)	(248)
Total Fair Value	26,449	35,397
Total Unrealized Losses	(270)	(248)
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	924
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(1)
Total Fair Value	924
Total Unrealized Losses	(1)
Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	21,607	14,364
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(1,200)	(1,564)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value	1,495	374
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses	(303)	(129)
Total Fair Value	23,102	14,738
Total Unrealized Losses	$ (1,503)	$ (1,693)

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Investments - Fair Value Measurements of Cash Equivalents Held in Money Market Funds and Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	$ 190,723	$ 201,133
Deferred Compensation Plan Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	14,596	12,834
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	66,412	57,614
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	11,774	26,424
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	10,206	19,239
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	13,004	15,373
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	29,767	35,398
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	3,730
Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	11,855
Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	24,100	12,967
Available-for-sale securities	190,723	201,133
Total	214,823	214,100
Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	6,878	1,271
Available-for-sale securities	73,742	82,483
Total	80,620	83,754
Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	17,222	11,696
Available-for-sale securities	116,981	118,650
Total	134,203	130,346
Fair Value, Measurements [Member] | Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	6,878	1,271
Fair Value, Measurements [Member] | Money Market Funds [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	6,878	1,271
Fair Value, Measurements [Member] | Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	17,222	11,696
Fair Value, Measurements [Member] | Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	17,222	11,696
Fair Value, Measurements [Member] | Deferred Compensation Plan Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	14,596	12,834
Fair Value, Measurements [Member] | Deferred Compensation Plan Assets [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	14,596	12,834
Fair Value, Measurements [Member] | Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	66,412	57,614
Fair Value, Measurements [Member] | Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	66,412	57,614
Fair Value, Measurements [Member] | Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	11,774	26,424
Fair Value, Measurements [Member] | Municipal Fixed-Rate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	11,774	26,424
Fair Value, Measurements [Member] | Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	10,206	19,239
Fair Value, Measurements [Member] | Asset-Backed Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	10,206	19,239
Fair Value, Measurements [Member] | Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	13,004	15,373
Fair Value, Measurements [Member] | Mortgage/Agency-Backed Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	13,004	15,373
Fair Value, Measurements [Member] | U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	29,767	35,398
Fair Value, Measurements [Member] | U.S. Government Bonds [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	29,767	35,398
Fair Value, Measurements [Member] | Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	3,730
Fair Value, Measurements [Member] | Foreign Government Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	3,730
Fair Value, Measurements [Member] | Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	11,855
Fair Value, Measurements [Member] | Variable Rate Demand Notes [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	11,855
Fair Value, Measurements [Member] | Marketable Equity Securities - Technology Industry [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	3,374	5,384
Fair Value, Measurements [Member] | Marketable Equity Securities - Technology Industry [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	3,374	5,384
Fair Value, Measurements [Member] | Marketable Equity Securities - Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	26,005	28,867
Fair Value, Measurements [Member] | Marketable Equity Securities - Other [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	$ 26,005	$ 28,867

XML

Derivative Instruments and Hedging Activities - Additional Information (Detail) - 12 months ended Dec. 31, 2016 - Forward Contracts [Member]	USD ($)	EUR (€)
Derivative [Line Items]
Derivative, notional amount	$ 5,800,000	€ 5,500,000
Derivative maturity year	2017

XML

Derivative Instruments and Hedging Activities - Schedule of Fair Values of Hedging Instruments Recorded in Consolidated Balance Sheet (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Significant Other Observable Inputs (Level 2) [Member] | Foreign Exchange Contracts [Member] | Other Receivables [Member]
Derivatives Not Designated as Hedging Instruments (Level 2):
Derivatives asset, fair value	$ 159

XML

Derivative Instruments and Hedging Activities - Schedule of Change in Fair Values of Derivative Instruments Recorded in Consolidated Statements of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Foreign Exchange Contracts [Member] | Other Income (Expense) [Member]
Derivatives Not Designated as Hedging Instruments:
Derivative instrument, gain or loss	$ 724	$ 511	$ 1,852

XML

Inventory - Components of Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
Raw materials	$ 40,461	$ 34,223
Work in process	4,003	2,893
Finished goods	60,653	54,417
Total Inventory, net	$ 105,117	$ 91,533

XML

Inventory - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Raw Materials [Member]
Inventory [Line Items]
Inventory valuation reserves	$ 14.6	$ 17.5
Finished Goods [Member]
Inventory [Line Items]
Inventory valuation reserves	$ 10.6	$ 9.2

XML

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Abstract]
Land	$ 4,575	$ 4,575
Building and land improvements	29,229	25,667
Building	68,301	68,301
Furniture and fixtures	18,477	17,347
Computer hardware and software	87,655	76,389
Engineering and other equipment	118,746	112,132
Total Property, Plant and Equipment	326,983	304,411
Less accumulated depreciation	(242,514)	(231,178)
Total Property, Plant and Equipment, net	$ 84,469	$ 73,233

XML

Property, Plant and Equipment - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Abstract]
Depreciation	$ 12.0	$ 12.3	$ 12.5

XML

Goodwill and Intangible Assets - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Goodwill [Line Items]
Goodwill	$ 3,492,000	$ 3,492,000
Number of reportable segments | Segment	2
Impairment losses	$ 0
Amortization expense	2,500,000	$ 1,900,000	$ 2,300,000
Network Solutions [Member]
Goodwill [Line Items]
Goodwill	3,100,000
Services & Support [Member]
Goodwill [Line Items]
Goodwill	$ 400,000

XML

Goodwill and Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Gross Value	$ 18,653	$ 14,169
Accumulated Amortization	(11,386)	(9,086)
Net Value	7,267	5,083
Customer Relationships [Member]
Goodwill [Line Items]
Gross Value	6,899	5,828
Accumulated Amortization	(3,208)	(2,627)
Net Value	3,691	3,201
Developed Technology [Member]
Goodwill [Line Items]
Gross Value	6,444	5,720
Accumulated Amortization	(5,061)	(4,329)
Net Value	1,383	1,391
Intellectual Property [Member]
Goodwill [Line Items]
Gross Value	2,340	2,340
Accumulated Amortization	(2,129)	(1,854)
Net Value	211	486
Supply Agreement [Member]
Goodwill [Line Items]
Gross Value	1,400
Accumulated Amortization	(544)
Net Value	856
License [Member]
Goodwill [Line Items]
Gross Value	500
Accumulated Amortization	(113)
Net Value	387
Patent [Member]
Goodwill [Line Items]
Gross Value	500
Accumulated Amortization	(20)
Net Value	480
Trade Names [Member]
Goodwill [Line Items]
Gross Value	370	270
Accumulated Amortization	(285)	(265)
Net Value	85	5
Non-compete [Member]
Goodwill [Line Items]
Gross Value	200	11
Accumulated Amortization	(26)	$ (11)
Net Value	$ 174

XML

Goodwill and Intangible Assets - Estimated Future Amortization Expense Related to Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Goodwill And Intangible Assets Disclosure [Abstract]
2017	$ 2,867
2018	1,168
2019	655
2020	621
2021	568
Thereafter	1,388
Net Value	$ 7,267	$ 5,083

XML

Alabama State Industrial Development Authority Financing and Economic Incentives - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2008	Jan. 13, 1995
Debt Instrument [Line Items]
Proceeds from state industrial development authority issued taxable bonds loaned to ADTRAN	$ 27,800			$ 50,000	$ 20,000
Percentage of interest on amended and restated bond	2.00%
Maturity date of amended and restated bond	Jan. 01, 2020
Estimated fair value of bond	$ 28,100
Restricted certificate of deposit held	27,800	$ 30,000
Total realized economic incentives	1,300	1,300	$ 1,300
Payments on long-term debt	1,100	$ 1,100	$ 16,500
Bond debt outstanding classified as current liability	1,000
Significant Other Observable Inputs (Level 2) [Member]
Debt Instrument [Line Items]
Estimated fair value of bond	$ 28,100

XML

Income Taxes - Summary of Components of Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current
Federal	$ 12,733	$ 7,504	$ 7,626
State	1,141	279	599
International	477	(29)	12,587
Total Current	14,351	7,754	20,812
Deferred
Federal	647	(585)	(1,083)
State	73	(66)	(123)
International	(3,405)	(41)	(4,320)
Total Deferred	(2,685)	(692)	(5,526)
Total Provision for Income Taxes	$ 11,666	$ 7,062	$ 15,286

XML

Income Taxes - Effective Income Tax Rate Differs from Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Tax provision computed at the federal statutory rate	35.00%	35.00%	35.00%
State income tax provision, net of federal benefit	3.93%	4.86%	2.69%
Federal research credits	(8.15%)	(12.55%)	(4.05%)
Foreign taxes	(0.34%)	2.10%	(7.26%)
Tax-exempt income	(0.53%)	(1.94%)	(1.25%)
State tax incentives	(2.77%)	(5.04%)	(2.21%)
Stock-based compensation	2.53%	6.91%	3.06%
Domestic production activity deduction	(2.23%)	(3.17%)	(1.15%)
Bargain purchase	(2.64%)
Other, net	0.08%	1.30%	0.69%
Effective Tax Rate	24.88%	27.47%	25.52%

XML

Income Taxes - Income Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
U.S. entities	$ 54,077	$ 27,400	$ 23,812
International entities	(7,182)	(1,692)	36,094
Income before provision for income taxes	$ 46,895	$ 25,708	$ 59,906

XML

Income Taxes - Principal Components of Current and Non-current Deferred Taxes (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Accounts receivable		$ 7
Inventory	$ 12,020	12,558
Accrued expenses	5,551	6,359
Investments	1,062
Deferred compensation	5,751	5,072
Stock-based compensation	4,724	4,704
Uncertain tax positions related to state taxes and related interest	762	1,026
Pensions	4,273	5,729
Foreign losses	6,486	5,389
State losses and credit carry-forwards	4,021	4,187
Federal loss and research carry-forwards	5,886	5,886
Valuation allowance	(6,149)	(7,250)
Total Deferred Tax Assets	44,387	43,667
Property, plant and equipment	(4,433)	(3,315)
Accrued expenses		(2,791)
Intellectual property	(1,918)	(476)
Investments		(70)
Total Deferred Tax Liabilities	(6,351)	(6,652)
Net Deferred Tax Assets	$ 38,036	$ 37,015

XML

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Line Items]
Deferred tax benefit recorded as an adjustment to other comprehensive income	$ 1,500	$ 3,700
Foreign and domestic carry-forwards, unamortized research and development cost and state credit carry-forwards	16,400
Net change in valuation allowance	1,100
Cash and cash equivalents	79,895	84,550	$ 73,439	$ 58,298
Short-term investments	43,188	34,396
Short-term liquidity amount	123,100	118,900
Income tax benefit (expense) from exercise of stock options adjustment to equity		(40)	100
Unrecognized tax benefits	2,226	2,537	3,334	$ 3,240
Unrecognized tax benefits, effective tax rate	1,700	1,800	2,600
Accrued interest and penalties	800	900	$ 1,000
Foreign Subsidiaries [Member]
Income Tax Disclosure [Line Items]
Short-term liquidity amount	$ 42,100	$ 38,900
Short-term liquidity, in percentage	34.20%	32.70%
Minimum [Member]
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration year	2017
Maximum [Member]
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration year	2030

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Income Taxes - Change in Unrecognized Income Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ 2,537	$ 3,334	$ 3,240
Increases for tax position related to, Prior years	95
Increases for tax position related to, Current year	428	280	522
Decreases for tax positions related to, Prior years		(29)
Settlements with taxing authorities		(103)
Expiration of applicable statute of limitations	(834)	(945)	(428)
Balance at end of period	$ 2,226	$ 2,537	$ 3,334

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Employee Benefit Plans (Pension Benefit Plan) - Schedule of Pension Benefit Plan Obligations and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	$ (26,851)	$ (30,507)
Service cost	(1,211)	(1,314)	$ (1,189)
Interest cost	(720)	(615)	(836)
Actuarial gain (loss) - experience	431	247
Actuarial gain (loss) - assumptions	(2,628)	2,078
Benefit payments	52	81
Effects of foreign currency exchange rate changes	916	3,179
Projected benefit obligation at end of period	(30,011)	(26,851)	(30,507)
Change in plan assets:
Fair value of plan assets at beginning of period	19,213	20,338
Actual return on plan assets	1,494	988
Effects of foreign currency exchange rate changes	(662)	(2,113)
Fair value of plan assets at end of period	20,045	19,213	$ 20,338
Funded (unfunded) status at end of period	$ (9,966)	$ (7,638)

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Employee Benefit Plans (Pension Benefit Plan) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 28.7	$ 25.1
Estimated amortization from accumulated other comprehensive income into net periodic pension cost in 2017	$ 0.3
Bond Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	75.00%
Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	25.00%
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Threshold for unamortized gain losses	10.00%

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Employee Benefit Plans (Pension Benefit Plan) - Summary of Net Amounts Recognized Balance Sheet for the Unfunded Pension Liability (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Current liability	$ 0	$ 0
Non-current liability	(9,966)	(7,638)
Total	$ (9,966)	$ (7,638)

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Employee Benefit Plans (Pension Benefit Plan) - Components of Net Periodic Pension Cost and Amounts Recognized Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net periodic benefit cost:
Service cost	$ 1,211	$ 1,314	$ 1,189
Interest cost	720	615	836
Expected return on plan assets	(1,057)	(1,011)	(1,086)
Amortization of actuarial losses	175	407
Net periodic benefit cost	1,049	1,325	939
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net actuarial (gain) loss	1,782	(2,303)	7,052
Amortization of actuarial losses	(156)	(396)
Amount recognized in other comprehensive income	1,626	(2,699)	7,052
Total recognized in net periodic benefit cost and other comprehensive income	$ 2,675	$ (1,374)	$ 7,991

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Employee Benefit Plans (Pension Benefit Plan) - Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Net actuarial loss	$ 6,871	$ 5,245

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Employee Benefit Plans (Pension Benefit Plan) - Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Discount rates	2.64%	2.20%	3.70%
Rate of compensation increase	2.00%	2.25%	2.25%
Expected long-term rates of return	5.40%	5.40%	5.40%

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Employee Benefit Plans (Pension Benefit Plan) - Weighted-Average Assumptions Used to Determine Benefit Obligation (Detail)	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Discount rates	1.90%	2.64%
Rate of compensation increase	2.00%	2.25%

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Employee Benefit Plans (Pension Benefit Plan) - Schedule of Pension Benefit Payments Expected Future Service (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Compensation And Retirement Disclosure [Abstract]
2017	$ 348
2018	515
2019	699
2020	964
2021	1,079
2022 – 2026	5,156
Total	$ 8,761

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Employee Benefit Plans (Pension Benefit Plan) - Schedule of Cash Equivalents and Investments Held at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	$ 190,723	$ 201,133
Total	20,045	19,213	$ 20,338
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	66,412	57,614
Pension Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash and cash equivalents	6	3
Available-for-sale securities	20,039	19,210
Total	20,045	19,213
Pension Benefit Plan [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	12,546	11,633
Pension Benefit Plan [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Cash and cash equivalents	6	3
Available-for-sale securities	20,039	19,210
Total	20,045	19,213
Pension Benefit Plan [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	12,546	11,633
Pension Benefit Plan [Member] | Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	2,037	1,960
Pension Benefit Plan [Member] | Government Bonds [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	2,037	1,960
Pension Benefit Plan [Member] | Large Cap Blend [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	4,462	4,604
Pension Benefit Plan [Member] | Large Cap Blend [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	4,462	4,604
Pension Benefit Plan [Member] | Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	249	258
Pension Benefit Plan [Member] | Large Cap Value [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	249	258
Pension Benefit Plan [Member] | Balanced Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	745	755
Pension Benefit Plan [Member] | Balanced Fund [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Available-for-sale securities	$ 745	$ 755

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Employee Benefit Plans (401(k) Savings Plan) - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation And Retirement Disclosure [Abstract]
Criteria of employer to contribute in employee saving plan	100% of an employee’s first 3% of contributions and 50% of their next 2% of contributions
Percentage of employer match to employee's contribution	100.00%
Percentage of employer match to employee's contribution	50.00%
Upper limit of employer match	4.00%
Maximum statutory compensation under code	$ 265,000
Percentage contributions under the savings plan, vested	100.00%
Contributions and plan administration costs for savings plan	$ 4,100,000	$ 4,700,000	$ 4,500,000

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Employee Benefit Plans (Deferred Compensation Plans) - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) Compensation_Program	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Compensation And Retirement Disclosure [Abstract]
Number of deferred compensation programs | Compensation_Program	4
Maximum percentage of cash compensation allowed to be deferred under the deferred compensation plan	25.00%
Criteria for benefit distribution	Six months after termination of employment in a single lump sum payment or annual installments paid over a three or ten year term.
Deferred compensation income (expense) adjustments due to fair value of the trust assets | $	$ (1.3)	$ 0.3	$ (0.7)

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Employee Benefit Plans (Deferred Compensation Plans) - Fair Value of Assets Held by Trust and Amounts Payable to Plan Participants (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Long-term Investments	$ 190,723	$ 201,133
Long-term Investments	14,596	12,834
Amounts Payable to Plan Participants Non-current Liabilities	14,596	12,834
Deferred Compensation Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term Investments	14,596	12,834
Non-Current Liabilities [Member]
Defined Benefit Plan Disclosure [Line Items]
Amounts Payable to Plan Participants Non-current Liabilities	$ 14,596	$ 12,834

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Employee Benefit Plans (Retiree Medical Coverage) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Maximum number of years medical, dental and prescription drug coverage to spouse of deceased officer	30 years
Total liability recorded to provide medical, dental and prescription drug coverage	$ 0.2	$ 0.2

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Segment Information and Major Customers - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) Customer Segment Category	Dec. 31, 2015 USD ($) Customer	Dec. 31, 2014 Customer
Segment Reporting Information [Line Items]
Number of reportable segments | Segment	2
Number of categories | Category	3
Number of single customer comprising more than 10% of revenue | Customer	3	3	2
Long-lived assets	$ 84.5	$ 73.2
United States [Member]
Segment Reporting Information [Line Items]
Long-lived assets	79.9	68.8
Outside United States [Member]
Segment Reporting Information [Line Items]
Long-lived assets	$ 4.6	$ 4.4
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customer 1 [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	24.00%	20.00%	21.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customer 2 [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	19.00%	17.00%	14.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customer 3 [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	12.00%	14.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | The Five Largest Customers Other Than Those With More Than 10% Of Revenues [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	13.00%	14.00%	22.00%

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Segment Information and Major Customers - Sales and Gross Profit of Market Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Sales	$ 162,986	$ 168,890	$ 162,701	$ 142,204	$ 139,013	$ 158,078	$ 160,138	$ 142,835	$ 636,781	$ 600,064	$ 630,007
Gross Profit	$ 70,787	$ 75,808	$ 78,955	$ 65,794	$ 62,439	$ 70,649	$ 68,246	$ 65,563	291,344	266,897	311,327
Network Solutions [Member]
Segment Reporting Information [Line Items]
Sales									525,502	527,422	559,532
Gross Profit									254,807	233,579	271,517
Services & Support [Member]
Segment Reporting Information [Line Items]
Sales									111,279	72,642	70,475
Gross Profit									$ 36,537	$ 33,318	$ 39,810

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Segment Information and Major Customers - Sales Information by Product Category (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customer [Line Items]
Sales	$ 162,986	$ 168,890	$ 162,701	$ 142,204	$ 139,013	$ 158,078	$ 160,138	$ 142,835	$ 636,781	$ 600,064	$ 630,007
Access & Aggregation [Member]
Revenue from External Customer [Line Items]
Sales									436,372	405,698	401,769
Customer Devices [Member]
Revenue from External Customer [Line Items]
Sales									137,608	125,565	138,051
Traditional & Other Products [Member]
Revenue from External Customer [Line Items]
Sales									$ 62,801	$ 68,801	$ 90,187

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Segment Information and Major Customers - Sales Information by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customer [Line Items]
Sales	$ 162,986	$ 168,890	$ 162,701	$ 142,204	$ 139,013	$ 158,078	$ 160,138	$ 142,835	$ 636,781	$ 600,064	$ 630,007
United States [Member]
Revenue from External Customer [Line Items]
Sales									501,337	419,366	381,382
Germany [Member]
Revenue from External Customer [Line Items]
Sales									85,780	111,666	150,987
Other International [Member]
Revenue from External Customer [Line Items]
Sales									$ 49,664	$ 69,032	$ 97,638

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Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) EquityUnit	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Contingencies And Commitments [Line Items]
Number of private equity funds | EquityUnit	2
Commitments towards private equity funds	$ 7.7
Operating leases expiration year	2025
Rental expense	$ 4.2	$ 4.9	$ 4.7
Investment Commitments [Member]
Contingencies And Commitments [Line Items]
Aggregate investment committed in private equity funds	7.9
Private Equity Funds [Member]
Contingencies And Commitments [Line Items]
Contribution to private equity funds	$ 8.4

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Commitments and Contingencies - Future Minimum Rental Payments under Non-Cancelable Operating Leases with Original Maturities of Greater than 12 Months (Detail) $ in Thousands	Dec. 31, 2016 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2017	$ 3,788
2018	2,043
2019	847
2020	741
Thereafter	3,243
Total	$ 10,662

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Earnings Per Share - Summary of Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator
Net Income	$ 7,572	$ 12,415	$ 10,228	$ 5,014	$ 5,718	$ 7,067	$ 2,544	$ 3,317	$ 35,229	$ 18,646	$ 44,620
Denominator
Weighted average number of shares – basic									48,724	51,145	55,120
Effect of dilutive securities:
Stock options									170	81	304
Restricted stock and restricted stock units									55	41	58
Weighted average number of shares – diluted									48,949	51,267	55,482
Net income per share – basic	$ 0.16	$ 0.26	$ 0.21	$ 0.10	$ 0.12	$ 0.14	$ 0.05	$ 0.06	$ 0.72	$ 0.36	$ 0.81
Net income per share – diluted	$ 0.16	$ 0.26	$ 0.21	$ 0.10	$ 0.12	$ 0.14	$ 0.05	$ 0.06	$ 0.72	$ 0.36	$ 0.80

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Earnings Per Share - Additional Information (Detail) - shares shares in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Anti-dilutive options, Total	4.6	6.1	4.4

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Summarized Quarterly Financial Data (Unaudited) - Quarterly Operating Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 162,986	$ 168,890	$ 162,701	$ 142,204	$ 139,013	$ 158,078	$ 160,138	$ 142,835	$ 636,781	$ 600,064	$ 630,007
Gross profit	70,787	75,808	78,955	65,794	62,439	70,649	68,246	65,563	291,344	266,897	311,327
Operating income	4,272	10,130	14,812	5,521	2,800	8,072	644	1,963	34,735	13,479	47,111
Net Income	$ 7,572	$ 12,415	$ 10,228	$ 5,014	$ 5,718	$ 7,067	$ 2,544	$ 3,317	$ 35,229	$ 18,646	$ 44,620
Earnings per common share – basic	$ 0.16	$ 0.26	$ 0.21	$ 0.10	$ 0.12	$ 0.14	$ 0.05	$ 0.06	$ 0.72	$ 0.36	$ 0.81
Earnings per common share – diluted	$ 0.16	$ 0.26	$ 0.21	$ 0.10	$ 0.12	$ 0.14	$ 0.05	$ 0.06	$ 0.72	$ 0.36	$ 0.80

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Related Party Transactions - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2014 USD ($)
Director Emeritus [Member]
Related Party Transaction
Related party legal fees	$ 0.1

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Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Feb. 24, 2017	Jan. 17, 2017	Dec. 31, 2016	Feb. 16, 2017
Subsequent Event [Line Items]
Dividend declaration date			Jan. 17, 2017
Dividend record date			Feb. 02, 2017
Dividend payment date			Feb. 16, 2017
Scenario Forecast [Member]
Subsequent Event [Line Items]
Stock repurchased, shares	200,000
Shares repurchased, average price per share	$ 21.46
Additional shares authorized for purchase	4,200,000
Subsequent Events [Member]
Subsequent Event [Line Items]
Common stock dividends per share declared		$ 0.09
Quarterly dividend payable subsequent to balance sheet date				$ 4.4

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Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 19	$ 136	$ 130
Charged to costs & expenses		19	23
Deductions	19	136	17
Balance at end of period		19	136
Inventory Reserve [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	26,675	24,682	22,993
Charged to costs & expenses	3,303	2,225	2,549
Deductions	4,729	232	860
Balance at end of period	25,249	26,675	24,682
Warranty Liability [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	8,739	8,415	8,977
Charged to costs & expenses	8,561	2,998	3,103
Deductions	8,752	2,674	3,665
Balance at end of period	8,548	8,739	8,415
Deferred Tax Asset Valuation Allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	7,250	7,463	8,842
Charged to costs & expenses	69	81	283
Deductions	1,170	294	1,662
Balance at end of period	$ 6,149	$ 7,250	$ 7,463