Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash Flows from Operating Activities:
Net income	$ 69,058	$ 46,025
Adjustments to reconcile net income to net cash provided (used) by operating activities:
Depreciation and amortization	20,307	18,546
Impairment charge		1,110
Benefit of deferred income taxes	1,941	2,520
Share-based compensation expense	5,655	4,922
Other	860	586
Tax benefit from share-based compensation arrangements (Note 2)		(2,063)
Changes in assets and liabilities:
Accounts receivable	(19,429)	(21,504)
Inventories	(5,369)	1,764
Other assets and liabilities	(38,531)	(23,752)
Accounts payable	(3,687)	(1,801)
Deferred revenue	469	637
Net cash provided by operating activities	31,274	26,990
Cash Flows from Investing Activities:
Purchases of property and equipment	(23,647)	(21,906)
Purchase of marketable securities	(90,492)	(72,079)
Proceeds from the sale and maturities of marketable securities	87,476	70,186
Acquisitions of a business, net of cash acquired	(2,349)
Net cash used by investing activities	(29,012)	(23,799)
Cash Flows from Financing Activities:
Borrowings on revolving credit facilities, net	60,000	49,000
Debt issue costs		(57)
Repurchases of common stock	(63,910)	(53,480)
Proceeds from exercises of stock options and employee stock purchase plans	12,526	5,760
Payment of acquisition-related contingent consideration		(2,084)
Shares withheld for statutory tax withholding on restricted stock (Note 2)	(7,303)	(3,764)
Tax benefit from share-based compensation arrangements (Note 2)		2,063
Net cash provided (used) by financing activities	1,313	(2,562)
Net effect of changes in exchange rates on cash	1,932	3,330
Net increase in cash and cash equivalents	5,507	3,959
Cash and cash equivalents at beginning of period	154,901	128,994
Cash and cash equivalents at end of period	$ 160,408	$ 132,953