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	$ 222,054	$ 192,135	$ 181,951
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	78,218	68,956	58,888
Amortization on marketable securities, net	843	1,432
Impairment charge	2,228	8,212
Provision for uncollectible accounts	1,170	2,200	2,035
Provision for deferred income taxes	20,881	5,143	830
Share-based compensation expense	19,891	19,884	18,099
Other	986	(472)	(160)
Tax benefit from share-based compensation arrangements	(14,702)	(11,315)	(16,078)
Changes in assets and liabilities:
Accounts receivable	(22,554)	(50,142)	(3,626)
Inventories	7,648	(34,969)	(38,310)
Accounts payable	2,117	(2,468)	6,703
Deferred revenue	7,672	(319)	14,195
Other assets and liabilities	8,119	18,087	11,319
Net cash provided by operating activities	334,571	216,364	235,846
Cash Flows from Investing Activities:
Purchases of property and equipment	(64,787)	(82,921)	(60,523)
Purchase of marketable securities	(227,894)	(271,958)
Proceeds from the sale and maturities of marketable securities	203,859	56,775
Proceeds from sale of equity investment			5,400
Acquisitions of intangible assets			(175)
Acquisitions of a businesses, net of cash acquired	(1,964)	(10,302)	(25,115)
Net cash used by investing activities	(90,786)	(308,406)	(80,413)
Cash Flows from Financing Activities:
Borrowings on revolving credit facilities, net	38,000	24,000	272,000
Issuance of senior notes		250,097	200,000
Debt issue costs	(56)	(1,380)	(1,406)
Payment of notes payable			(1,394)
Repurchases of common stock	(304,086)	(401,981)	(618,158)
Proceeds from exercises of stock options and employee stock purchase plans	38,344	22,397	29,442
Payment of acquisition-related contingent consideration	(4,728)
Tax benefit from share-based compensation arrangements	14,702	11,315	16,078
Net cash used by financing activities	(217,824)	(95,552)	(103,438)
Net effect of changes in exchange rates on cash	(54)	(5,948)	(8,517)
Net increase (decrease) in cash and cash equivalents	25,907	(193,542)	43,478
Cash and cash equivalents at beginning of period	128,994	322,536	279,058
Cash and cash equivalents at end of period	$ 154,901	$ 128,994	$ 322,536