Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net income	$ 138,702	$ 148,493
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	175,739	165,783
Stock-based compensation	80,255	66,652
Provision for deferred income taxes	39,368	2,785
Amortization of debt discount and issuance costs	9,243	9,292
Other non-cash reconciling items, net	1,609	3,501
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	(17,873)	17,786
Prepaid expenses and other current assets	(50,108)	(10,991)
Accounts payable and accrued expenses	(17,541)	12,282
Deferred revenue	10,406	12,126
Other current liabilities	5,901	6,971
Other non-current assets and liabilities	(8,450)	1,062
Net cash provided by operating activities	367,251	435,742
Cash flows from investing activities:
Cash paid for acquired businesses, net of cash acquired	(197,201)	0
Purchases of property and equipment	(104,881)	(86,820)
Capitalization of internal-use software development costs	(83,305)	(73,661)
Purchases of short- and long-term marketable securities	(181,219)	(384,585)
Proceeds from sales of short- and long-term marketable securities	180,215	50,541
Proceeds from maturities of short- and long-term marketable securities	232,901	301,802
Other non-current assets and liabilities	(1,249)	(1,512)
Net cash used in investing activities	(154,739)	(194,235)
Cash flows from financing activities:
Proceeds related to the issuance of common stock under stock plans	25,680	27,095
Employee taxes paid related to net share settlement of stock-based awards	(41,338)	(32,410)
Repurchases of common stock	(177,615)	(199,710)
Other non-current assets and liabilities	(1,096)	0
Net cash used in financing activities	(194,369)	(205,025)
Effects of exchange rate changes on cash and cash equivalents	10,189	689
Net increase in cash and cash equivalents	28,332	37,171
Cash and cash equivalents at beginning of period	324,169	289,473
Cash and cash equivalents at end of period	352,501	326,644
Supplemental disclosure of cash flow information:
Cash paid for income taxes, net of refunds received in the six months ended June 30, 2017 and 2016 of $2,481 and $457, respectively	54,146	38,228
Non-cash investing activities:
Purchases of property and equipment and capitalization of internal-use software development costs included in accounts payable and accrued expenses	14,026	11,424
Capitalization of stock-based compensation	$ 46,988	$ 28,113