CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities
Net income	$ 36,769	$ 53,664
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	7,775	7,455
Stock-based compensation expense	3,192	3,363
Loss (gain) on sale of equipment	(13)	(63)
Deferred income taxes	(962)	(2,755)
Changes in operating assets and liabilities:
Trade receivables, net	(8,942)	62,837
Inventories, net	1,899	(7,010)
Prepaids and other assets	8,050	(1,259)
Excess tax benefits of stock options and awards	(11)	(24)
Accounts payable and accrued expenses	4,766	(29,139)
Net cash provided by operating activities	52,523	87,069
Investing activities
Purchase of property, plant and equipment	(7,732)	(6,156)
Proceeds from sale of equipment	76	121
Net cash used in investing activities	(7,656)	(6,035)
Financing activities
Repurchase of common stock	0	0
Proceeds from exercise of stock options	155	282
Excess tax benefits of stock options and awards	11	24
Net cash used in financing activities	166	306
Effect of exchange rate changes on cash activities	(3,003)	(5,914)
Increase (decrease) in cash and cash equivalents	42,030	75,426
Cash and cash equivalents at beginning of period	381,336	298,705
Cash and cash equivalents at end of period	$ 423,366	$ 374,131