Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash Flows from Operating Activities:
Net income	$ 103,516	$ 103,837
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	32,944	28,089
Provision for uncollectible accounts	1,448	788
Benefit of deferred income taxes	(2,055)	(5,225)
Share-based compensation expense	9,642	8,820
Other	417	110
Tax benefit from share-based compensation arrangements	(8,746)	(7,960)
Changes in assets and liabilities:
Accounts receivable	(57,126)	(9,786)
Inventories	(16,023)	(5,575)
Other assets	32,792	(2,950)
Accounts payable	(2,992)	337
Accrued liabilities	(27,589)	(3,344)
Deferred revenue	(706)	8,139
Net cash provided by operating activities	65,522	115,280
Cash Flows from Investing Activities:
Purchases of property and equipment	(46,873)	(25,410)
Purchase of marketable securities	(190,370)
Proceeds from the sale and maturities of marketable securities	10,039
Proceeds from sale of equity investment		5,400
Acquisitions of a businesses, net of cash acquired	(383)	(1,161)
Acquisition of intangible asset		(175)
Net cash used by investing activities	(227,587)	(21,346)
Cash Flows from Financing Activities:
(Repayments) borrowings on revolving credit facilities, net	(51,000)	107,000
Debt issue costs	(127)	(1,156)
Issuance of long term debt	250,097
Payment of notes payable		(1,394)
Repurchases of common stock	(220,097)	(196,626)
Proceeds from exercises of stock options and employee stock purchase plans	15,650	14,707
Tax benefit from share-based compensation arrangements	8,746	7,960
Net cash provided (used) by financing activities	3,269	(69,509)
Net effect of changes in exchange rates on cash	(588)	1,565
Net (decrease) increase in cash and cash equivalents	(159,384)	25,990
Cash and cash equivalents at beginning of period	322,536	279,058
Cash and cash equivalents at end of period	$ 163,152	$ 305,048