Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income (loss)	$ 26,639	$ (108,173)	$ (121,510)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	30,294	41,770	54,315
Stock-based compensation expense	64,515	107,461	131,575
(Gain) loss from sales of investments, assets and other, net	(238)	26	(5,558)
Tax benefits from stock-based awards			989
Excess tax (benefits) from stock-based awards			(989)
Accretion and amortization on marketable securities	(636)	323	5,711
Change in deferred income taxes and other	3,780	(1,988)	(12,693)
Impairment of intangible assets		20,677
Changes in operating assets and liabilities:
Accounts receivable, net	(26,417)	3,834	10,148
Other assets	(8,124)	(2,501)	(18,096)
Accounts payable	(3,666)	(3,613)	10,934
Deferred revenue	(7,581)	13,113	(64,762)
Income tax payable	4,788	1,889
Other liabilities	11,223	(12,802)	(34,511)
Net cash provided by (used in) operating activities	94,577	60,016	(44,447)
Cash flows from investing activities:
Purchases of short-term investments	(348,594)		(101,091)
Sales and maturities of short-term investments	40,000	244,837	867,198
Acquisition of property and equipment	(9,971)	(10,313)	(7,832)
Business acquisitions, net of cash acquired	(133,701)	(33,630)	(20,023)
Proceeds from sale of property and equipment	273	3,209	814
Proceeds from sale of equity method investment			10,507
Other investing activities, net	(8,163)
Net cash provided by (used in) investing activities	(460,156)	204,103	749,573
Cash flows from financing activities:
Taxes paid related to net share settlement of stockholders' equity awards	(21,719)	(3,422)	(2,902)
Repurchases of common stock	(105,013)	(142,596)	(88,409)
Proceeds from issuance of common stock	8,769	5,921	7,567
Excess tax benefits from stock-based awards			989
Acquisition-related contingent consideration payment		(10,230)	(10,790)
Net cash provided by (used in) financing activities	(117,963)	(150,327)	(93,545)
Effect of exchange rate changes on cash and cash equivalents	3,945	(3,542)	(667)
Net increase (decrease) in cash and cash equivalents	(479,597)	110,250	610,914
Cash and cash equivalents, beginning of period	852,467	742,217	131,303
Cash and cash equivalents, end of period	372,870	852,467	742,217
Supplemental cash flow information:
Income taxes paid	$ 4,024	$ 1,033	$ 2,803