Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating Activities
Net income	$ 24,011	$ 26,276
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	7,281	6,346
Amortization of bond premiums	29	151
Provision for losses on accounts receivable, net of adjustments	141	(42)
Provision for excess and obsolete inventories	260	308
Share-based compensation	3,529	2,043
Loss (gain) on disposal of assets	47	(20)
Foreign currency transaction gain	(24)	(48)
Interest income on note receivable	(13)	(14)
Deferred	364	(1,851)
Changes in assets and liabilities:
Accounts receivable	(254)	(8,417)
Income taxes	5,430	4,033
Inventories	(15,983)	(1,934)
Prepaid expenses and other	(272)	(550)
Accounts payable	6,801	1,848
Deferred revenue	118	220
Accrued liabilities and donations	2,295	1,252
Net cash provided by operating activities	33,760	29,601
Investing Activities
Capital expenditures	(16,847)	(15,825)
Proceeds from sale of property, plant and equipment	7	1
Investment in certificates of deposits	(5,280)	(4,112)
Maturities of certificates of deposits	5,272	6,000
Purchases of investments held to maturity	(13,241)	(9,782)
Maturities of investments	14,063	3,801
Proceeds from called investments	500	1,010
Principal payments from note receivable	26	26
Net cash used in investing activities	(15,500)	(18,881)
Financing Activities
Borrowings under revolving credit facility	0	761
Payments under revolving credit facility	0	(761)
Stock options exercised	1,573	1,255
Repurchase of stock	(9,368)	(7,233)
Employee taxes paid by withholding shares	(1,066)	(441)
Net cash used in financing activities	(8,861)	(6,419)
Net increase in cash and cash equivalents	9,399	4,301
Cash and cash equivalents, beginning of period	24,153	7,908
Cash and cash equivalents, end of period	$ 33,552	$ 12,209