Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash Flows from Operating Activities:
Net income	$ 147,745	$ 156,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	51,227	43,610
Amortization on marketable securities, net	967
Impairment charge	8,212
Provision for uncollectible accounts	1,808	1,678
Benefit of deferred income taxes	(4,649)	(6,729)
Share-based compensation expense	14,760	13,463
Other	(305)	(79)
Tax benefit from share-based compensation arrangements	(10,044)	(9,581)
Changes in assets and liabilities:
Accounts receivable	(51,024)	(8,464)
Inventories	(27,238)	(12,638)
Other assets	41,041	(3,375)
Accounts payable	(2,841)	6,876
Accrued liabilities	(24,503)	16,216
Deferred revenue	(2,688)	11,566
Net cash provided by operating activities	142,468	208,543
Cash Flows from Investing Activities:
Purchases of property and equipment	(67,517)	(42,504)
Purchase of marketable securities	(231,387)
Proceeds from the sale and maturities of marketable securities	24,711
Proceeds from sale of equity investment		5,400
Acquisitions of a businesses, net of cash acquired	(8,200)	(7,516)
Acquisition of intangible asset		(175)
Net cash used by investing activities	(282,393)	(44,795)
Cash Flows from Financing Activities:
(Repayments) borrowings on revolving credit facilities, net	(6,500)	98,000
Debt issue costs	(199)	(1,357)
Issuance of long term debt	250,097	200,000
Payment of notes payable		(1,394)
Repurchases of common stock	(309,057)	(468,968)
Proceeds from exercises of stock options and employee stock purchase plans	19,221	18,361
Tax benefit from share-based compensation arrangements	10,044	9,581
Net cash used by financing activities	(36,394)	(145,777)
Net effect of changes in exchange rates on cash	(5,067)	(4,294)
Net (decrease) increase in cash and cash equivalents	(181,386)	13,677
Cash and cash equivalents at beginning of period	322,536	279,058
Cash and cash equivalents at end of period	$ 141,150	$ 292,735