Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income (loss)	$ (10,895)	$ 34,950
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	11,952	12,034
Amortization of net premium on available-for-sale investments	(14)	352
Net gain on long-term investments	(5,400)	(2,869)
Net (gain) loss on disposal of property, plant and equipment	68	(10)
Gain on bargain purchase of a business	(11,322)
Stock-based compensation expense	5,243	5,573
Deferred income taxes	(20,368)
Changes in operating assets and liabilities:
Accounts receivable, net	41,166	(6,975)
Other receivables	(1,842)	(2,924)
Inventory	16,543	(9,483)
Prepaid expenses and other assets	8,722	(9,647)
Accounts payable	5,223	(4,727)
Accrued expenses and other liabilities	156	(2,820)
Income tax payable	9,461	8,571
Net cash provided by operating activities	48,693	22,025
Cash flows from investing activities:
Purchases of property, plant and equipment	(5,695)	(12,304)
Proceeds from disposals of property, plant and equipment		16
Proceeds from sales and maturities of available-for-sale investments	116,757	137,272
Purchases of available-for-sale investments	(115,271)	(79,713)
Acquisition of business	(7,806)
Net cash provided by (used in) investing activities	(12,015)	45,271
Cash flows from financing activities:
Proceeds from stock option exercises	1,321	6,606
Purchases of treasury stock	(14,185)	(17,348)
Dividend payments	(12,976)	(13,031)
Net cash used in financing activities	(25,840)	(23,773)
Net increase in cash and cash equivalents	10,838	43,523
Effect of exchange rate changes	(3,098)	4,835
Cash and cash equivalents, beginning of period	86,433	79,895
Cash and cash equivalents, end of period	94,173	128,253
Supplemental disclosure of non-cash investing activities:
Purchases of property, plant and equipment included in accounts payable	$ 355	$ 272