Share-Based Compensation - Additional Information (Detail)	12 Months Ended
Dec. 31, 2016 USD ($) $ / shares Plans shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of share-based compensation plans \| Plans	2
Closing sale price per share \| $ / shares	$ 20.90	$ 32.51	$ 42.16
Stock options granted			5,538
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Payout based on economic profit performance against target economic profit goals	0.00%	0.00%	0.00%
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Payout based on economic profit performance against target economic profit goals	200.00%	200.00%	200.00%
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost \| $	$ 0
Stock options granted	0	0
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock and restricted stock units granted	554,491	462,697	253,042
Diluted earnings per share required to determine specific performance measure of stock awards \| $ / shares	$ 0.50
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost \| $	$ 16,800,000
Restricted stock and restricted stock units granted	276,110	162,092	176,717
Vesting period, in years			3 years
Vesting year	2019	2018
Share-based compensation, weighed -average period for recognition	2 years
Non Employee Directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense, directors fees \| $	$ 100,000	$ 100,000	$ 100,000
Accumulated number of stock units outstanding	40,189	41,051	43,082
Restricted stock and restricted stock units granted	55,120	30,778	20,664
Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock and restricted stock units granted	383,196	333,268	271,594
Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock and restricted stock units granted	392,285	260,743	137,501
Terms of granting restricted stock and restricted stock units	the officer is still employed as of the anniversary date of the grant, and the Company’s cumulative diluted earnings per share for the four calendar quarters immediately preceding the vesting date exceed $0.50 per diluted share as defined in the officers’ restricted stock agreement.

The number of share-based compensation plans outstanding during the period.

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Share based compensation arrangement by share based payment award, award vesting year.

+ References

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Amount of diluted earnings per share required to be attained over the previous four quarters immediately preceding the vesting date for use in determining achievement of specific performance measure of equity-based compensation awards.

+ References

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Share based compensation arrangement by share based payment payout percentage.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Noninterest expense related to directors' fees which are fees paid by an Entity to its directors. Directors' fees may be paid in addition to salary and other benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.14)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Gross number of share options (or share units) granted during the period.

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- Definition

Description of pertinent provisions of equity-based compensation awards that have actual or potential impact upon the company's financial statements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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