Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities
Net income	$ 79,009	$ 53,711	$ 42,329
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	25,634	22,766	17,655
Amortization of bond premiums	0	0	13
Amortization of debt issuance costs	43	7	0
Provision for credit losses on accounts receivable, net of adjustments	153	91	174
Provision for excess and obsolete inventories	1,108	1,454	152
Share-based compensation	11,342	11,799	7,862
(Gain) loss on disposition of assets	(6,478)	337	(12)
Foreign currency transaction (gain) loss	(12)	(27)	55
Interest income on note receivable	(24)	(25)	(27)
Deferred income taxes	13,027	6,038	2,641
Changes in assets and liabilities:
Accounts receivable	19,859	(13,412)	(2,832)
Income tax receivable	(3,815)	5,129	(4,448)
Inventories	(9,726)	2,557	(5,598)
Prepaid expenses and other	(2,364)	(329)	(528)
Accounts payable	(2,155)	280	(1,176)
Deferred revenue	1,010	425	412
Accrued liabilities and donations	2,203	7,124	(1,816)
Net cash provided by operating activities	128,814	97,925	54,856
Investing Activities
Capital expenditures	(67,802)	(37,166)	(37,268)
Cash paid in business combination	0	0	(6,377)
Proceeds from sale of property, plant and equipment	60	69	13
Insurance proceeds	6,417	0	0
Investment in certificates of deposits	0	(6,000)	(7,200)
Maturities of certificates of deposits	0	6,000	10,080
Purchase of investments held to maturity	0	0	(9,001)
Maturities of investments held to maturity	0	0	14,570
Proceeds from called investments	0	0	495
Principal payments from note receivable	52	51	53
Net cash used in investing activities	(61,273)	(37,046)	(34,635)
Financing Activities
Proceeds from financing obligation, net of issuance costs	0	6,614	0
Payment related to financing costs	0	(301)	0
Stock options exercised	21,418	12,625	4,987
Repurchase of stock	(30,060)	(19,586)	(26,846)
Employee taxes paid by withholding shares	(1,169)	(1,207)	(1,097)
Dividends paid to stockholders	(19,815)	(16,645)	(16,728)
Net cash used in financing activities	(29,626)	(18,500)	(39,684)
Net increase (decrease) in cash, cash equivalents and restricted cash	37,915	42,379	(19,463)
Cash, cash equivalents and restricted cash, beginning of year	44,373	1,994	21,457
Cash, cash equivalents and restricted cash, end of year	$ 82,288	$ 44,373	$ 1,994