Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 199,214	$ 224,493
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	272,917	250,294
Stock-based compensation	122,103	105,304
Provision (benefit) for deferred income taxes	25,302	(13,861)
Amortization of debt discount and issuance costs	13,989	13,958
Other non-cash reconciling items, net	3,655	8,367
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(19,199)	22,477
Prepaid expenses and other current assets	(34,195)	4,014
Accounts payable and accrued expenses	22,150	54,892
Deferred revenue	991	6,885
Other current liabilities	3,651	4,670
Other non-current assets and liabilities	(7,036)	6,097
Net cash provided by operating activities	603,542	687,590
Cash flows from investing activities:
Cash paid for acquired businesses, net of cash acquired	(197,201)	(2,936)
Purchases of property and equipment	(185,466)	(134,874)
Capitalization of internal-use software development costs	(122,460)	(105,477)
Purchases of short- and long-term marketable securities	(249,098)	(614,808)
Proceeds from sales of short- and long-term marketable securities	180,405	57,900
Proceeds from maturities of short- and long-term marketable securities	317,974	498,633
Other non-current assets and liabilities	(1,895)	(3,145)
Net cash used in investing activities	(257,741)	(304,707)
Cash flows from financing activities:
Proceeds related to the issuance of common stock under stock plans	41,740	42,339
Employee taxes paid related to net share settlement of stock-based awards	(48,122)	(38,560)
Repurchases of common stock	(306,629)	(294,867)
Other non-current assets and liabilities	(1,096)	0
Net cash used in financing activities	(314,107)	(291,088)
Effects of exchange rate changes on cash and cash equivalents	12,289	535
Net increase in cash and cash equivalents	43,983	92,330
Cash and cash equivalents at beginning of period	324,169	289,473
Cash and cash equivalents at end of period	368,152	381,803
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds received in the nine months ended September 30, 2017 and 2016 of $5,867 and $1,582, respectively	79,479	64,716
Non-cash investing activities:
Capitalization of stock-based compensation	29,546	35,176
Purchases of property and equipment and capitalization of internal-use software development costs included in accounts payable and accrued expenses	$ 21,602	$ 17,086