Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities:
Net income	$ 72,800	$ 71,487
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	53,516	42,375
Stock-based compensation	25,114	22,931
Provision for doubtful accounts	87	320
Excess tax benefits from stock-based compensation	(15,178)	(4,119)
Provision for deferred income taxes	1,660	0
Amortization of debt discount and issuance costs	1,941	0
Loss (gain) from disposal of property and equipment	215	(71)
Gain from divestiture of a business	0	(1,188)
Changes in operating assets and liabilities, net of effects of acquisitions and divestitures:
Accounts receivable	(18,137)	(28,355)
Prepaid expenses and other current assets	(20,961)	(11,447)
Accounts payable and accrued expenses	(22,511)	(4,528)
Deferred revenue	5,159	8,225
Other current liabilities	1,287	(111)
Other non-current assets and liabilities	4,031	(2,295)
Net cash provided by operating activities	89,023	93,224
Cash flows from investing activities:
Cash paid for acquired businesses, net of cash acquired	(386,647)	0
Purchases of property and equipment	(52,011)	(43,831)
Capitalization of internal-use software development costs	(31,995)	(16,998)
Purchases of short- and long-term marketable securities	(658,943)	(145,350)
Proceeds from sales of short- and long-term marketable securities	297,059	55,509
Proceeds from maturities of short- and long-term marketable securities	102,911	66,171
Proceeds from the sale of property and equipment	166	260
Other non-currents assets and liabilities	(998)	0
Net cash used in investing activities	(730,458)	(84,239)
Cash flows from financing activities:
Proceeds from the issuance of convertible senior notes, net of issuance costs	679,603	0
Proceeds from the issuance of warrants related to convertible senior notes	77,970	0
Purchase of note hedge related to convertible senior notes	(101,292)	0
Payment of acquired debt and capital leases	(17,862)	0
Proceeds related to the issuance of common stock under stock plans	44,329	10,364
Excess tax benefits from stock-based compensation	15,178	4,119
Employee taxes paid related to net share settlement of stock-based awards	(26,271)	(17,315)
Repurchases of common stock	(116,147)	(40,278)
Net cash provided by (used in) financing activities	555,508	(43,110)
Effects of exchange rate changes on cash and cash equivalents	762	(2,589)
Net decrease in cash and cash equivalents	(85,165)	(36,714)
Cash and cash equivalents at beginning of period	333,891	201,989
Cash and cash equivalents at end of period	248,726	165,275
Supplemental disclosure of cash flow information:
Cash paid for income taxes	54,479	16,097
Non-cash financing and investing activities:
Purchases of property and equipment and capitalization of internal-use software development costs included in accrued expenses	20,093	18,136
Capitalization of stock-based compensation	3,784	2,938
Convertible note receivable received for divestiture of a business	$ 0	$ 18,882