Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net income	$ 3,279	$ 193,582	$ 175,635
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	240,171	61,969	47,131
Stock-based compensation expense	78,943	46,661	46,149
Excess tax benefits from stock-based compensation exercises	0	0	(13,860)
Deferred taxes	(217,414)	(2,648)	344
Gain on extinguishment of debt	0	(2,500)	0
Amortization and write-off of deferred financing fees	15,062	3,082	1,512
Changes in assets and liabilities, net of acquisitions:
Fees receivable, net	(368,516)	(68,661)	(44,476)
Deferred commissions	(61,393)	(18,673)	(13,236)
Prepaid expenses and other current assets	13,251	(21,604)	(13,268)
Other assets	(18,529)	20,005	(14,733)
Deferred revenues	382,852	97,979	91,840
Accounts payable, accrued, and other liabilities	186,811	56,440	82,523
Cash provided by operating activities	254,517	365,632	345,561
Investing activities:
Additions to property, equipment and leasehold improvements	(110,765)	(49,863)	(46,128)
Acquisitions - cash paid (net of cash acquired)	(2,634,809)	(34,186)	(196,229)
Cash used in investing activities	(2,745,574)	(84,049)	(242,357)
Financing activities:
Proceeds from employee stock purchase plan	11,711	9,250	7,499
Proceeds from borrowings	3,025,000	715,000	440,000
Payments for deferred financing fees	(51,171)	(4,975)	0
Payments on borrowings	(404,438)	(835,000)	(20,000)
Purchases of treasury stock	(41,272)	(58,961)	(509,049)
Excess tax benefits from stock-based compensation exercises	0	0	13,860
Net Cash Provided by (Used in) Financing Activities	2,539,830	(174,686)	(67,690)
Net increase in cash and cash equivalents	48,773	106,897	35,514
Effects of exchange rates on cash and cash equivalents	25,902	(5,640)	(27,840)
Cash and cash equivalents, beginning of period	474,233	372,976	365,302
Cash and cash equivalents, end of period	548,900	474,233	372,976
Cash paid during the period for:
Interest	98,500	23,400	21,200
Income taxes, net of refunds received	$ 76,100	$ 86,300	$ 83,500