Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income	$ 96,775	$ 131,335
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	210,393	175,739
Stock-based compensation	92,183	80,255
(Benefit) provision for deferred income taxes	(12,116)	35,223
Amortization of debt discount and issuance costs	13,759	9,243
Restructuring-related software charges	2,818	0
Other non-cash reconciling items, net	8,015	1,609
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(16,889)	(4,265)
Prepaid expenses and other current assets	8,578	(51,224)
Accounts payable and accrued expenses	(27,091)	(17,541)
Deferred revenue	29,552	9,811
Other current liabilities	5,655	5,901
Other non-current assets and liabilities	59	(8,835)
Net cash provided by operating activities	411,691	367,251
Cash flows from investing activities:
Cash paid for acquired businesses, net of cash acquired	(79)	(197,201)
Purchases of property and equipment	(98,300)	(104,881)
Capitalization of internal-use software development costs	(103,409)	(83,305)
Purchases of short- and long-term marketable securities	(467,886)	(181,219)
Proceeds from sales of short- and long-term marketable securities	16,196	180,215
Proceeds from maturities of short- and long-term marketable securities	124,370	232,901
Other non-current assets and liabilities	(479)	(1,143)
Net cash used in investing activities	(529,587)	(154,633)
Cash flows from financing activities:
Proceeds from the issuance of convertible senior notes	1,132,622	0
Proceeds from the issuance of warrants	119,945	0
Purchase of note hedge related to convertible senior notes	(261,740)	0
Proceeds related to the issuance of common stock under stock plans	34,103	25,680
Employee taxes paid related to net share settlement of stock-based awards	(41,308)	(41,338)
Repurchases of common stock	(185,512)	(177,615)
Other non-current assets and liabilities	(4,844)	(1,096)
Net cash provided by (used in) financing activities	793,266	(194,369)
Effects of exchange rate changes on cash, cash equivalents and restricted cash	(11,460)	10,252
Net increase in cash, and cash equivalents and restricted cash	663,910	28,501
Cash, cash equivalents and restricted cash at beginning of period	314,429	324,626
Cash, cash equivalents and restricted cash at end of period	978,339	353,127
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds received of $8,656 and $2,481 for the six months ended June 30, 2018 and 2017, respectively	28,088	54,146
Non-cash investing activities:
Purchases of property and equipment and capitalization of internal-use software development costs included in accounts payable and accrued expenses	16,891	14,026
Capitalization of stock-based compensation	$ 34,016	$ 46,988