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	$ 77,640	$ 70,009
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	62,090	58,539
Amortization of original issue discount and deferred financing costs	2,861	2,672
(Gain) loss on foreign currency transactions	(56)	273
Non-cash revenue and other	(29)	(137)
(Gain) loss on disposal of fixed assets	(79)	280
Stock-based compensation	8,476	6,900
Deferred rent	1,614	2,304
Deferred income taxes	(4,729)	5,263
Changes in assets and liabilities:
Accounts receivable	13,963	11,388
Prepaid expenses and other current assets	49	(19,267)
Accounts payable and accrued expenses	(1,814)	16,380
Deferred revenue	(3,531)	(12,732)
Accrued rent and related obligations	6,880	1,917
Other assets	1,157	(3,919)
Other current and long-term liabilities	461	2,393
Net cash provided by operating activities	164,953	142,263
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of fixed assets, net	(50,466)	(61,415)
Payments for acquisitions, net of cash acquired	(22,307)	(66,636)
Net cash used in investing activities	(72,773)	(128,051)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under revolving line of credit	270,500	118,100
Repayments under revolving line of credit	(264,500)	(91,600)
Principal payments of long-term debt	(7,163)	(7,163)
Payments for debt issuance costs	(1,002)	0
Purchase of treasury stock	(95,677)	(117,538)
Taxes paid related to net share settlement of stock options	(7,747)	0
Proceeds from issuance of common stock upon exercise of options	9,148	7,452
Proceeds from issuance of restricted stock	3,682	3,864
Payments of contingent consideration for acquisitions	(750)	0
Tax benefit from stock-based compensation	10,484	6,379
Net cash used in financing activities	(83,025)	(80,506)
Effect of exchange rates on cash and cash equivalents	(1,210)	(199)
Net increase (decrease) in cash and cash equivalents	7,945	(66,493)
Cash and cash equivalents—beginning of period	11,539	87,886
Cash and cash equivalents—end of period	19,484	21,393
NON-CASH TRANSACTION:
Fixed asset purchases recorded in accounts payable and accrued expenses	3,000	3,500
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash payments of interest	28,752	28,429
Cash payments of taxes	$ 29,405	$ 43,153