Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 80,930	$ 74,858
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	86,533	80,669
Stock-based compensation	38,986	31,741
Provision for deferred income taxes	31,972	1,072
Amortization of debt discount and issuance costs	4,597	4,653
Other non-cash reconciling items, net	(129)	2,752
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(30,146)	15,906
Prepaid expenses and other current assets	(47,065)	(3,481)
Accounts payable and accrued expenses	(23,940)	(32,377)
Deferred revenue	10,876	10,653
Other current liabilities	3,516	6,876
Other non-current assets and liabilities	(13,512)	(1,949)
Net cash provided by operating activities	142,618	191,373
Cash flows from investing activities:
Cash paid for acquired businesses, net of cash acquired	(10)	0
Purchases of property and equipment	(45,224)	(41,806)
Capitalization of internal-use software development costs	(45,957)	(40,534)
Purchases of short- and long-term marketable securities	(92,306)	(95,843)
Proceeds from sales of short- and long-term marketable securities	180,257	0
Proceeds from maturities of short- and long-term marketable securities	143,881	125,109
Other non-current assets and liabilities	(1,230)	(2,354)
Net cash provided by (used in) investing activities	139,411	(55,428)
Cash flows from financing activities:
Proceeds related to the issuance of common stock under stock plans	17,530	18,350
Employee taxes paid related to net share settlement of stock-based awards	(33,921)	(26,496)
Repurchases of common stock	(72,467)	(108,725)
Net cash used in financing activities	(88,858)	(116,871)
Effects of exchange rate changes on cash and cash equivalents	4,979	4,365
Net increase in cash and cash equivalents	198,150	23,439
Cash and cash equivalents at beginning of period	324,169	289,473
Cash and cash equivalents at end of period	522,319	312,912
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds received in the three months ended March 31, 2017 of $0.8 million	41,133	28,010
Non-cash investing activities:
Purchases of property and equipment and capitalization of internal-use software development costs included in accounts payable and accrued expenses	39,200	19,518
Capitalization of stock-based compensation	$ 6,411	$ 5,203