Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating activities:
Net income	$ 23,608	$ 11,406
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation	2,485	2,422
Warrant-related stock-based compensation		4,286
(Gain) loss on derivative instrument	(348)	272
Depreciation and amortization of intangible assets	6,112	4,575
Excess tax benefits from stock-based award activity	(17,842)	(12,058)
Deferred income taxes	(6,668)	(5,462)
Unrealized amortization of premium on investments, net	391	(327)
Amortization of debt issuance costs	107	331
Accretion of debt discount	161	135
Other	55	26
Cash Provided (used) by changes in operating assets and liabilities:
Accounts receivable	(6,225)	2,971
Other receivables	(284)	657
Prepaid expenses and other current assets	3,587	(1,564)
Other long-term assets	(114)	1,863
Accounts payable	3,122	(3,713)
Deferred revenue	1,122	2,054
Accrued expenses and other current and long-term liabilities	22,486	11,174
Net cash provided by operating activities	31,755	19,048
Investing Activities:
Business acquisitions, net of cash acquired		(279,386)
Equity investment in privately - held company	(4,000)
Purchases of property and equipment	(1,543)	(193)
Change in restricted cash	231	767
Proceeds from sales of investments		163,883
Proceeds from maturities of investments	18,718	20,020
Purchases of investments	(62,077)
Net cash used by investing activities	(48,671)	(94,909)
Financing Activities:
Proceeds from issuance of convertible debt, net of debt issuance costs of $6,037	195,213
Proceeds from loan, net of debt issuance costs of $2,343 and debt discount of $953		96,704
Repayment of debt		(15,000)
Excess tax benefits from stock-based award activity	17,842	12,058
Proceeds from stock option exercises	293	2,063
Proceeds from issuance of stock through employee stock purchase plan	461	189
Tax payments from shares withheld upon vesting of restricted stock units	(536)	(210)
Net cash provided by financing activities	213,273	95,804
Net increase (decrease) in cash and cash equivalents	196,357	19,943
Cash and cash equivalents:
Beginning of period	68,278	81,897
End of period	264,635	101,840
Cash paid for:
Income tax expense	395	371
Interest expense	738	364
Supplemental disclosure of non-cash financing activities:
Purchases of assets through leasehold incentives	$ 1,006