Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash Flows from Operating Activities:
Net income	$ 291,370	$ 224,979
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	62,574	61,620
Impairment charge	2,629	0
Benefit of (provision for) deferred income taxes	12,850	(438)
Share-based compensation expense	18,948	17,762
Other	2,385	1,912
Changes in assets and liabilities:
Accounts receivable	(33,041)	(18,724)
Inventories	(27,415)	(22,966)
Other assets and liabilities	(58,214)	(10,734)
Accounts payable	(1,336)	(3,540)
Deferred revenue	(6,314)	2,279
Net cash provided by operating activities	264,436	252,150
Cash Flows from Investing Activities:
Purchases of property and equipment	(82,642)	(54,370)
Purchase of marketable securities	(87)	(269,798)
Proceeds from the sale and maturities of marketable securities	284,125	224,816
Acquisitions of intangible assets	(450)	(320)
Acquisitions of a business, net of cash acquired	(22,500)	(14,529)
Net cash provided (used) by investing activities	178,446	(114,201)
Cash Flows from Financing Activities:
(Repayments) borrowings on revolving credit facilities, net	(240,500)	75,250
Payment of acquisition-related contingent consideration	(1,266)	0
Repurchases of common stock	(263,712)	(228,693)
Proceeds from exercises of stock options and employee stock purchase plans	34,595	31,314
Shares withheld for statutory tax withholding on restricted stock	(9,110)	(7,829)
Net cash used by financing activities	(479,993)	(129,958)
Net effect of changes in exchange rates on cash	(3,687)	6,127
Net (decrease) increase in cash and cash equivalents	(40,798)	14,118
Cash and cash equivalents at beginning of period	187,675	154,901
Cash and cash equivalents at end of period	$ 146,877	$ 169,019