CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net income	$ 126,096	$ 118,467
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	34,876	39,135
Deferred income tax expense	3,382	3,275
Provision for bad debts	695	833
Stock-based compensation expense	15,612	16,861
Excess tax benefits from stock-based compensation	(3,768)	(5,703)
Other	(141)	(134)
Changes in operating assets and liabilities:
Accounts receivable	6,121	11,252
Other receivables and current assets	22,021	25,497
Other long-term assets	(705)	15
Accounts payable, accrued expenses and current liabilities	(25,627)	(33,726)
Accrued income taxes	2,438	2,263
Deferred revenue	5,245	10,839
Other long-term liabilities	(7,641)	(8,342)
Net cash provided by operating activities	178,604	180,532
Cash flows from investing activities:
Acquisitions, net of cash acquired	0	(10,376)
Capital expenditures	(6,068)	(7,682)
Other investing activities	(10,256)	(111)
Net cash used in investing activities	(16,324)	(18,169)
Cash flows from financing activities:
Purchase of treasury stock	(128,760)	(128,716)
Restricted stock withholding taxes paid in lieu of issued shares	(5,004)	(4,382)
Contingent consideration payments	(1,048)	(1,173)
Proceeds from shares issued for stock-based compensation	17,419	29,675
Excess tax benefits from stock-based compensation	3,768	5,703
Other financing activities	(1)	(10)
Net cash used in financing activities	(113,626)	(98,903)
Effect of exchange rate fluctuations on cash and cash equivalents	10,533	(11,170)
Net increase in cash and cash equivalents	59,187	52,290
Cash and cash equivalents, beginning of period	784,168	788,064
Cash and cash equivalents, end of period	843,355	840,354
Supplemental disclosures of cash flow information:
Income taxes paid	65,873	55,018
Interest paid	$ 727	$ 609