Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 298,373	$ 222,766	$ 320,727
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	434,520	372,313	334,302
Stock-based compensation	183,813	164,308	144,506
Provision (benefit) for deferred income taxes	2,339	(7,244)	9,629
Amortization of debt discount and issuance costs	41,958	18,839	18,638
Restructuring-related software charge	4,940	31,965	4,587
Other non-cash reconciling items, net	12,078	10,068	5,987
Changes in operating assets and liabilities, net of effects of acquisitions and divestitures:
Accounts receivable	(30,445)	(50,054)	(2,970)
Prepaid expenses and other current assets	(4,132)	(28,968)	42,145
Accounts payable and accrued expenses	42,238	33,232	18,491
Deferred revenue	(919)	2,938	(3,512)
Other current liabilities	9,422	16,378	5,484
Other non-current assets and liabilities	14,142	14,442	(26,202)
Net cash provided by operating activities	1,008,327	800,983	871,812
Cash flows from investing activities:
Cash paid for acquisitions, net of cash acquired	(79)	(369,073)	(95,439)
Purchases of property and equipment	(217,609)	(254,146)	(180,949)
Capitalization of internal-use software development costs	(188,132)	(160,632)	(135,340)
Purchases of short- and long-term marketable securities	(873,697)	(326,497)	(781,061)
Proceeds from sales of short and long-term marketable securities	16,569	219,916	57,740
Proceeds from maturities of short and long-term marketable securities	758,481	432,853	664,837
Other non-current assets and liabilities	(2,066)	(1,586)	786
Net cash used in by investing activities	(506,533)	(459,165)	(469,426)
Cash flows from financing activities:
Proceeds from the issuance of convertible senior notes	1,132,185	0	0
Proceeds from the issuance of warrants	119,945	0	0
Purchase of note hedge related to convertible senior notes	(261,740)	0	0
Proceeds related to the issuance of common stock under stock plans	62,608	55,680	59,560
Employee taxes paid related to net share settlement of stock-based awards	(64,305)	(58,395)	(45,545)
Repurchases of common stock	(750,000)	(361,194)	(373,794)
Other non-current assets and liabilities	(5,085)	(1,096)	0
Net cash used in financing activities	233,608	(365,005)	(359,779)
Effects of exchange rate changes on cash and cash equivalents	(12,844)	12,990	(7,891)
Net increase (decrease) in cash and cash equivalents	722,558	(10,197)	34,716
Cash, cash equivalents and restricted cash at beginning of year	314,429	324,626	289,910
Cash, cash equivalents and restricted cash at end of year	1,036,987	314,429	324,626
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds received in the years ended December 31, 2018, 2017 and 2016 of $18,501, $6,750 and $1,664, respectively	45,129	91,640	120,233
Non-cash financing and investing activities:
Purchases of property and equipment and capitalization of internal-use software development costs included in accounts payable and accrued expenses	54,867	27,209	36,742
Capitalization of stock-based compensation	$ 34,785	$ 28,851	$ 23,093