Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flow from operating activities:
Net income	$ 51,250	$ 48,147
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	61,372	58,557
Stock-based compensation expense	12,702	10,900
Amortization and write-offs of loan origination costs	2,626	2,656
Loss on extinguishment of debt		2,326
Loss on sale or disposition of property and equipment	28	10
Deferred income taxes	(12,425)	(7,295)
Provision for doubtful accounts	44	1,154
Changes in operating assets and liabilities, excluding effects from acquisitions:
Accounts receivable	(19,818)	(7,087)
Prepaid expenses and other assets	(30)	(2,532)
Contract assets	26,847
Accounts payable	(10,548)	6,106
Accrued expenses	(54,389)	(72,908)
Income taxes prepaid and payable	19,680	5,077
Deferred revenue	(7,395)	12,777
Net cash provided by operating activities	69,944	57,888
Cash flow from investing activities:
Additions to property and equipment	(7,163)	(5,990)
Cash paid for business acquisitions, net of cash acquired	(191)	1,805
Additions to capitalized software	(3,945)	(3,277)
Net cash used in investing activities	(11,299)	(7,462)
Cash flow from financing activities:
Cash received from debt borrowings	45,000	45,000
Repayments of debt	(106,250)	(105,200)
Proceeds from exercise of stock options	29,132	14,017
Withholding taxes paid related to equity award net share settlement	(2,171)	(589)
Fees paid for debt extinguishment		(1,363)
Dividends paid on common stock	(14,504)	(12,715)
Net cash used in financing activities	(48,793)	(60,850)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	119	1,663
Net increase (decrease) in cash, cash equivalents and restricted cash	9,971	(8,761)
Cash, cash equivalents and restricted cash, beginning of period	64,649	119,674
Cash, cash equivalents and restricted cash, end of period	$ 74,620	$ 110,913