Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 53,714	$ 74,583
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	104,095	86,533
Stock-based compensation	44,686	38,986
(Benefit) provision for deferred income taxes	(7,814)	28,425
Amortization of debt discount and issuance costs	4,850	4,597
Restructuring-related software charges	2,818	0
Other non-cash reconciling items, net	4,379	(129)
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(18,419)	(19,876)
Prepaid expenses and other current assets	(4,927)	(47,172)
Accounts payable and accrued expenses	(31,312)	(23,940)
Deferred revenue	25,243	10,043
Other current liabilities	13,701	3,516
Other non-current assets and liabilities	996	(12,948)
Net cash provided by operating activities	192,010	142,618
Cash flows from investing activities:
Cash paid for acquired businesses, net of cash acquired	(79)	(10)
Purchases of property and equipment	(51,584)	(45,224)
Capitalization of internal-use software development costs	(61,491)	(45,957)
Purchases of short- and long-term marketable securities	(73,352)	(92,306)
Proceeds from sales of short- and long-term marketable securities	16,196	180,257
Proceeds from maturities of short- and long-term marketable securities	59,540	143,881
Other non-current assets and liabilities	(715)	(335)
Net cash (used in) provided by investing activities	(111,485)	140,306
Cash flows from financing activities:
Proceeds related to the issuance of common stock under stock plans	22,738	17,530
Employee taxes paid related to net share settlement of stock-based awards	(29,714)	(33,921)
Repurchases of common stock	(19,785)	(72,467)
Other non-current assets and liabilities	(3,900)	0
Net cash used in financing activities	(30,661)	(88,858)
Effects of exchange rate changes on cash, cash equivalents and restricted cash	1,165	5,019
Net increase in cash, and cash equivalents and restricted cash	51,029	199,085
Cash, cash equivalents and restricted cash at beginning of period	314,429	324,626
Cash, cash equivalents and restricted cash at end of period	365,458	523,711
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds received of $4,476 and $815 for the three months ended March 31, 2018 and 2017, respectively	18,313	41,133
Non-cash investing activities:
Purchases of property and equipment and capitalization of internal-use software development costs included in accounts payable and accrued expenses	7,811	6,411
Capitalization of stock-based compensation	$ 18,555	$ 39,200