Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Activities
Net income	$ 10,902	$ 4,260
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	5,914	4,129
Amortization of bond premiums	0	5
Provision for losses on accounts receivable, net of adjustments	115	(11)
Provision for excess and obsolete inventories	357	101
Share-based compensation	2,030	1,724
Loss (gain) on disposal of assets	284	(7)
Foreign currency transaction gain	(16)	3
Interest income on note receivable	(6)	9
Deferred	1,887	420
Changes in assets and liabilities:
Accounts receivable	(4,725)	(2,897)
Income taxes	1,348	(5,673)
Inventories	2,678	3,447
Prepaid expenses and other	(561)	(712)
Accounts payable	(5,730)	9,833
Deferred revenue	25	37
Accrued liabilities and donations	411	(3,924)
Net cash provided by operating activities	14,913	10,744
Investing Activities
Capital expenditures	(8,772)	(8,451)
Cash paid in business combination	0	(6,000)
Proceeds from sale of property, plant and equipment	52	6
Investment in certificates of deposits	0	(4,320)
Maturities of certificates of deposits	0	1,200
Purchases of investments held to maturity	0	(7,495)
Maturities of investments	0	4,230
Proceeds from called investments	0	395
Principal payments from note receivable	17	14
Net cash used in investing activities	(8,703)	(20,421)
Financing Activities
Stock options exercised	4,010	1,340
Repurchase of stock	(4,483)	(4,379)
Employee taxes paid by withholding shares	(588)	(568)
Net cash used in financing activities	(1,061)	(3,607)
Net increase (decrease) in cash and cash equivalents	5,149	(13,284)
Cash and cash equivalents, beginning of period	1,994	21,457
Cash and cash equivalents, end of period	$ 7,143	$ 8,173