Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net income		$ 452,385	$ 362,431	$ 368,707
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation		36,456	30,462	21,097
Stock-based compensation		63,946	90,122	37,649
Provision for losses on accounts receivable		35,885	24,629	24,412
Amortization of deferred financing costs and discounts		7,582	7,049	2,796
Loss on extinguishment of debt		0	0	15,764
Amortization of intangible assets		161,635	159,740	86,149
Amortization of premium on receivables		5,165	3,250	3,259
Deferred income taxes		(28,681)	30,626	41,716
Equity method investment loss		36,356	57,668	8,586
Other non-cash operating expenses		(690)	(4,242)	(27,501)
Changes in operating assets and liabilities (net of acquisitions):
Restricted cash		(2,306)	(35,676)	6,625
Accounts receivable		(338,796)	40,017	246,465
Prepaid expenses and other current assets		5,301	(12,564)	2,820
Other assets		(20,345)	(2,524)	12,455
Excess tax benefits related to stock-based compensation		0	(26,427)	(56,790)
Accounts payable, accrued expenses and customer deposits		292,019	30,023	(185,875)
Net cash provided by operating activities		705,912	754,584	608,334
Investing activities
Acquisitions, net of cash acquired1	[1]	(1,331,985)	(49,069)	(2,395,778)
Purchases of property and equipment		(59,011)	(41,875)	(27,070)
Other		1,411	(8,470)	(171,239)
Net cash used in investing activities		(1,389,585)	(99,414)	(2,594,087)
Financing activities
Excess tax benefits related to stock-based compensation		0	26,427	56,790
Proceeds from issuance of common stock		21,231	19,926	29,641
(Payments) borrowings on securitization facility, net		(23,000)	(61,000)	326,000
Repurchase of common stock		(187,678)	0	0
Deferred financing costs paid		(2,272)	0	(43,943)
Proceeds from notes payable		600,000	0	2,320,000
Principal payments on notes payable		(118,500)	(103,500)	(546,875)
Borrowings (payments) from swing line of credit, net		26,606	(546)	4,990
Payment of contingent consideration		0	(42,177)	0
Other		(676)	(377)	(731)
Net cash provided by (used in) financing activities		753,969	(648,065)	2,162,265
Effect of foreign currency exchange rates on cash		(42,430)	(37,022)	(37,548)
Net increase (decrease) in cash		27,866	(29,917)	138,964
Cash and cash equivalents, beginning of year		447,152	477,069	338,105
Cash and cash equivalents, end of year		475,018	447,152	477,069
Supplemental cash flow information
Cash paid for interest		70,339	72,537	29,098
Cash paid for income taxes		101,951	83,380	79,124
Revolving A Facility
Financing activities
Borrowings from revolver —A Facility		1,225,107	0	807,330
Payments on revolver and foreign revolver facilities		(786,849)	(486,818)	(783,600)
Revolving B Facility
Financing activities
Payments on revolver and foreign revolver facilities		$ 0	$ 0	$ (7,337)

[1] Amounts reported in acquisitions and investment, net of cash acquired, includes debt assumed and immediately repaid in acquisitions.