Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net income	$ 148,493	$ 144,946
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	165,783	144,449
Stock-based compensation	66,652	61,920
Excess tax benefits from stock-based compensation	(2,632)	(22,737)
Provision (benefit) for deferred income taxes	2,785	(16,275)
Amortization of debt discount and issuance costs	9,292	9,253
Other non-cash reconciling items, net	3,501	1,146
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	17,786	(14,292)
Prepaid expenses and other current assets	(10,991)	12,022
Accounts payable and accrued expenses	12,282	31,673
Deferred revenue	12,126	7,023
Other current liabilities	6,971	199
Other non-current assets and liabilities	1,062	4,425
Net cash provided by operating activities	433,110	363,752
Cash flows from investing activities:
Cash paid for acquired businesses, net of cash acquired	0	(122,945)
Purchases of property and equipment	(86,820)	(159,495)
Capitalization of internal-use software development costs	(73,661)	(73,587)
Purchases of short- and long-term marketable securities	(384,585)	(405,989)
Proceeds from sales of short- and long-term marketable securities	50,541	2,008
Proceeds from maturities of short- and long-term marketable securities	301,802	527,677
Other non-current assets and liabilities	(1,512)	(1,909)
Net cash used in investing activities	(194,235)	(234,240)
Cash flows from financing activities:
Proceeds related to the issuance of common stock under stock plans	27,095	36,512
Excess tax benefits from stock-based compensation	2,632	22,737
Employee taxes paid related to net share settlement of stock-based awards	(32,410)	(39,354)
Repurchases of common stock	(199,710)	(126,068)
Other non-current assets and liabilities	0	(1,250)
Net cash used in financing activities	(202,393)	(107,423)
Effects of exchange rate changes on cash and cash equivalents	689	(3,291)
Net increase in cash and cash equivalents	37,171	18,798
Cash and cash equivalents at beginning of period	289,473	238,650
Cash and cash equivalents at end of period	326,644	257,448
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds received in the six months ended June 30, 2016 and 2015 of $457 and $17,964, respectively	38,228	12,055
Non-cash investing activities:
Purchases of property and equipment and capitalization of internal-use software development costs included in accounts payable and accrued expenses	28,113	41,874
Capitalization of stock-based compensation	$ 11,424	$ 8,615