Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating Activities
Net income	$ 30,036	$ 38,728
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	12,865	11,025
Amortization of bond premiums	11	39
Provision for losses on accounts receivable, net of adjustments	67	180
Provision for excess and obsolete inventories	55	54
Share-based compensation	5,614	4,960
(Gain) loss on disposal of assets	(9)	46
Foreign currency transaction gain	(20)	(65)
Interest income on note receivable	27	(18)
Deferred	864	1,147
Changes in assets and liabilities:
Accounts receivable	146	(14,521)
Income taxes	(649)	6,239
Inventories	(7,071)	(18,819)
Prepaid expenses and other	(792)	(141)
Accounts payable	4,328	3,781
Deferred revenue	(1,644)	416
Accrued liabilities and donations	364	8,814
Net cash provided by operating activities	44,192	41,865
Investing Activities
Capital expenditures	(34,328)	(26,436)
Cash paid in business combination	(6,377)	0
Proceeds from sale of property, plant and equipment	11	8
Investment in certificates of deposits	(7,200)	(5,280)
Maturities of certificates of deposits	7,920	5,752
Purchases of investments held to maturity	(9,001)	(13,241)
Maturities of investments	13,320	15,443
Proceeds from called investments	495	500
Principal payments from note receivable	32	48
Net cash used in investing activities	(35,128)	(23,206)
Financing Activities
Stock options exercised	3,504	1,715
Repurchase of stock	(17,500)	(12,991)
Employee taxes paid by withholding shares	(860)	(1,193)
Cash dividends paid to stockholders	(8,400)	(6,828)
Net cash used in financing activities	(23,256)	(19,297)
Net decrease in cash and cash equivalents	(14,192)	(638)
Cash and cash equivalents, beginning of period	21,457	24,153
Cash and cash equivalents, end of period	$ 7,265	$ 23,515