Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net income	$ 35,229	$ 18,646	$ 44,620
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,407	14,245	14,845
Amortization of net premium on available-for-sale investments	643	2,402	4,360
Net realized gain on long-term investments	(5,923)	(10,337)	(7,278)
Net loss on disposal of property, plant and equipment	22	644	142
Gain on bargain purchase of a business	(3,542)
Stock-based compensation expense	6,695	6,712	8,563
Deferred income taxes	(2,685)	(692)	(5,526)
Tax impact of stock option exercises		(40)	81
Excess tax benefits from stock-based compensation arrangements	(2)	(3)	(63)
Change in operating assets and liabilities:
Accounts receivable, net	(21,302)	14,918	(3,910)
Other receivables	4,101	11,704	(19,298)
Inventory	(10,887)	(6,877)	2,144
Prepaid expenses and other assets	(7,108)	(5,070)	(3,818)
Accounts payable	26,722	(5,826)	9,973
Accrued expenses and other liabilities	8,792	(10,289)	(166)
Income taxes payable, net	(3,162)	(11,590)	11,168
Net cash provided by operating activities	42,000	18,547	55,837
Cash flows from investing activities
Purchases of property, plant and equipment	(21,441)	(11,753)	(11,256)
Proceeds from disposals of property, plant and equipment		183	1
Proceeds from sales and maturities of available-for-sale investments	225,075	280,435	230,019
Purchases of available-for-sale investments	(209,172)	(188,921)	(142,695)
Acquisition of business	(943)
Net cash provided by (used in) investing activities	(6,481)	79,944	76,069
Cash flows from financing activities
Proceeds from stock option exercises	4,717	961	2,839
Purchases of treasury stock	(25,817)	(66,160)	(80,576)
Dividend payments	(17,583)	(18,449)	(19,947)
Payments on long-term debt	(1,100)	(1,100)	(16,500)
Excess tax benefits from stock-based compensation arrangements	2	3	63
Net cash used in financing activities	(39,781)	(84,745)	(114,121)
Net increase (decrease) in cash and cash equivalents	(4,262)	13,746	17,785
Effect of exchange rate changes	(393)	(2,635)	(2,644)
Cash and cash equivalents, beginning of year	84,550	73,439	58,298
Cash and cash equivalents, end of year	79,895	84,550	73,439
Supplemental disclosure of cash flow information
Cash paid during the year for interest	575	598	758
Cash paid during the year for income taxes	18,689	20,139	9,856
Supplemental disclosure of non-cash investing activities
Purchases of property, plant and equipment included in accounts payable	$ 2,103	$ 598	$ 467