CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 195,653	$ 184,500
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	52,320	58,782
Deferred income tax benefit	(3,102)	(7,301)
Provision for bad debts	1,006	1,286
Stock-based compensation expense	24,564	25,731
Excess tax benefits from stock-based compensation	(6,178)	(6,366)
Other	(211)	1,473
Changes in operating assets and liabilities:
Accounts receivable	6,601	6,707
Other receivables and current assets	26,431	35,330
Other long-term assets	(80)	396
Accounts payable, accrued expenses and current liabilities	(23,622)	(33,255)
Accrued income taxes	4,674	2,389
Deferred revenue	(12,178)	(6,557)
Other long-term liabilities	(5,285)	(4,788)
Net cash provided by operating activities	260,593	258,327
Cash flows from investing activities:
Acquisitions, net of cash acquired	0	(40,892)
Capital expenditures	(8,219)	(10,765)
Other investing activities	(11,355)	(2)
Net cash used in investing activities	(19,574)	(51,659)
Cash flows from financing activities:
Purchase of treasury stock	(243,288)	(242,748)
Restricted stock withholding taxes paid in lieu of issued shares	(5,044)	(4,431)
Contingent consideration payments	(1,048)	(1,173)
Proceeds from shares issued for stock-based compensation	43,347	36,563
Excess tax benefits from stock-based compensation	6,178	6,366
Other financing activities	(1)	(15)
Net cash used in financing activities	(199,856)	(205,438)
Effect of exchange rate fluctuations on cash and cash equivalents	12,585	(13,055)
Net increase (decrease) in cash and cash equivalents	53,748	(11,825)
Cash and cash equivalents, beginning of period	784,168	788,064
Cash and cash equivalents, end of period	837,916	776,239
Supplemental disclosures of cash flow information:
Income taxes paid	95,066	77,867
Interest paid	791	609
Fair value of stock options and restricted stock awards assumed in connection with acquisitions	$ 0	$ 3,528