Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities
Net income	$ 53,711	$ 42,329	$ 53,830
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	22,766	17,655	15,007
Amortization of bond premiums	0	13	47
Amortization of debt issuance costs	7	0	0
Provision for losses on accounts receivable, net of adjustments	91	174	179
Provision for excess and obsolete inventories	1,454	152	264
Share-based compensation	11,799	7,862	6,313
Loss (gain) on disposition of assets	337	(12)	45
Foreign currency transaction (gain) loss	(27)	55	(59)
Interest income on note receivable	(25)	(27)	(25)
Deferred income taxes	6,038	2,641	(749)
Changes in assets and liabilities:
Accounts receivable	(13,412)	(2,832)	(7,516)
Income tax receivable	5,129	(4,448)	4,591
Inventories	2,557	(5,598)	(23,698)
Prepaid expenses and other	(329)	(528)	98
Accounts payable	280	(1,176)	3,043
Deferred revenue	425	412	258
Accrued liabilities and donations	7,124	(1,816)	6,366
Net cash provided by operating activities	97,925	54,856	57,994
Investing Activities
Capital expenditures	(37,166)	(37,268)	(41,713)
Cash paid in business combination	0	(6,377)	0
Proceeds from sale of property, plant and equipment	69	13	10
Investment in certificates of deposits	(6,000)	(7,200)	(5,280)
Maturities of certificates of deposits	6,000	10,080	7,912
Purchase of investments held to maturity	0	(9,001)	(13,241)
Maturities of investments held to maturity	0	14,570	19,700
Proceeds from called investments	0	495	1,500
Principal payments from note receivable	51	53	60
Net cash used in investing activities	(37,046)	(34,635)	(31,052)
Financing Activities
Proceeds from financing obligation, net of issuance costs	6,614	0	0
Payment related to financing costs	(301)	0	0
Stock options exercised	12,625	4,987	2,259
Repurchase of stock	(19,586)	(26,846)	(16,620)
Employee taxes paid by withholding shares	(1,207)	(1,097)	(1,614)
Cash dividends paid to stockholders	(16,645)	(16,728)	(13,663)
Net cash used in financing activities	(18,500)	(39,684)	(29,638)
Net increase (decrease) in cash, cash equivalents and restricted cash	42,379	(19,463)	(2,696)
Cash, cash equivalents and restricted cash, beginning of year	1,994	21,457	24,153
Cash, cash equivalents and restricted cash, end of year	$ 44,373	$ 1,994	$ 21,457