CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net income	$ 72,906	$ 92,877
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	15,500	15,139
Stock-based compensation expense	6,254	6,482
(Gain) loss on sale of equipment	(29)	75
Deferred income taxes	(3,828)	(4,935)
Changes in operating assets and liabilities:
Trade receivables, net	64,200	70,508
Inventories, net	763	3,348
Prepaids and other assets	20,658	(2,958)
Excess tax benefits of stock options and awards	(26)	(57)
Accounts payable and accrued expenses	(13,537)	(67,468)
Net cash provided by operating activities	162,861	113,011
Investing activities
Purchase of property, plant and equipment	(15,276)	(11,204)
Proceeds from sale of equipment	139	136
Net cash used in investing activities	(15,137)	(11,068)
Financing activities
Repurchase of common stock	(24,238)	(19,943)
Proceeds from exercise of stock options	508	1,952
Excess tax benefits of stock options and awards	26	57
Net cash used in financing activities	(23,704)	(17,934)
Effect of exchange rate changes on cash activities	(13,627)	(41)
Increase in cash and cash equivalents	110,393	83,968
Cash and cash equivalents at beginning of period	381,336	298,705
Cash and cash equivalents at end of period	$ 491,729	$ 382,673