Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Operating Activities
Net income	$ 32,780	$ 33,625
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	8,587	8,660
Amortization of bond premiums	168	561
Provision for losses on accounts receivable, net of adjustments	(48)	(59)
Provision for excess and obsolete inventories, net	(111)	223
Share-based compensation	2,076	1,578
Excess tax benefits from stock options exercised and restricted stock awards vested	(2,217)	(908)
Gain on disposal of assets	(59)	(24)
Foreign currency transaction loss	114	36
Interest income on note receivable	(23)	(30)
Deferred income taxes	(1,000)	(4,361)
Changes in assets and liabilities:
Accounts receivable	(1,685)	(15,663)
Income tax receivable	2,614	1,981
Inventories	(3,323)	(5,323)
Prepaid expenses and other	(154)	(486)
Accounts payable	(3,801)	5,982
Deferred revenue	138	591
Accrued liabilities and donations	2,130	12,761
Net cash provided by operating activities	36,186	39,144
Investing Activities
Capital expenditures	(12,775)	(13,567)
Proceeds from sale of property, plant and equipment	63	30
Investment in certificates of deposits	(6,200)	(9,940)
Maturities of certificates of deposits	4,658	6,745
Purchases of investments held to maturity	(14,183)	(6,880)
Maturities of investments	9,907	8,891
Proceeds from called investments	757	2,525
Principal payments from note receivable	42	52
Net cash used in investing activities	(17,731)	(12,144)
Financing Activities
Stock options exercised	2,640	908
Excess tax benefits from stock options exercised and restricted stock awards vested	2,217	908
Repurchase of stock	(9,436)	(17,309)
Cash dividends paid to stockholders	(5,965)	(4,773)
Net cash used in financing activities	(10,544)	(20,266)
Net increase in cash and cash equivalents	7,911	6,734
Cash and cash equivalents, beginning of period	21,952	12,085
Cash and cash equivalents, end of period	$ 29,863	$ 18,819