Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net income	$ 74,858	$ 77,746
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	80,669	70,460
Stock-based compensation	31,741	29,669
Excess tax benefits from stock-based compensation	(1,135)	(13,128)
Provision for deferred income taxes	1,072	8,305
Amortization of debt discount and issuance costs	4,653	4,576
Other non-cash reconciling items, net	2,752	443
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	15,906	(32,552)
Prepaid expenses and other current assets	(3,481)	(1,817)
Accounts payable and accrued expenses	(32,377)	(52,703)
Deferred revenue	10,653	6,947
Other current liabilities	6,876	42
Other non-current assets and liabilities	(1,949)	1,741
Net cash provided by operating activities	190,238	99,729
Cash flows from investing activities:
Cash paid for acquired businesses, net of cash acquired	0	(16,062)
Purchases of property and equipment	(41,806)	(91,924)
Capitalization of internal-use software development costs	(40,534)	(45,145)
Purchases of short- and long-term marketable securities	(95,843)	(97,304)
Proceeds from sales of short- and long-term marketable securities	0	2,008
Proceeds from maturities of short- and long-term marketable securities	125,109	305,647
Other non-current assets and liabilities	(2,354)	(82)
Net cash (used in) provided by investing activities	(55,428)	57,138
Cash flows from financing activities:
Proceeds related to the issuance of common stock under stock plans	18,350	24,440
Excess tax benefits from stock-based compensation	1,135	13,128
Employee taxes paid related to net share settlement of stock-based awards	(26,496)	(31,101)
Repurchases of common stock	(108,725)	(62,680)
Net cash used in financing activities	(115,736)	(56,213)
Effects of exchange rate changes on cash and cash equivalents	4,365	(6,747)
Net increase in cash and cash equivalents	23,439	93,907
Cash and cash equivalents at beginning of period	289,473	238,650
Cash and cash equivalents at end of period	312,912	332,557
Supplemental disclosure of cash flow information:
Cash paid for income taxes	28,010	24,131
Non-cash investing activities:
Purchases of property and equipment and capitalization of internal-use software development costs included in accounts payable and accrued expenses	19,518	31,565
Capitalization of stock-based compensation	$ 5,203	$ 4,144