Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net income	$ 266,745	$ 233,290	$ 122,456
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	218,984	211,779	255,601
Stock-based compensation expense	62,540	69,008	66,172
Deferred taxes	(53,190)	(55,787)	1,524
Loss (gain) from divested operations	0	2,075	(45,447)
Loss on extinguishment of debt	44,814	0	0
Gain on sale of an equity security	0	(9,120)	0
Reduction in the carrying amount of operating lease right-of-use assets	81,851	86,466	0
Amortization and write-off of deferred financing fees	8,424	6,497	13,815
Amortization of deferred swap losses from de-designation	10,320	0	0
Gain on de-designated swaps	(2,157)	0	0
Changes in assets and liabilities, net of acquisitions and divestitures:
Fees receivable, net	99,409	(66,729)	(115,003)
Deferred commissions	8,656	(30,315)	(31,247)
Prepaid expenses and other current assets	37,895	18,985	(50,551)
Other assets	(8,950)	(27,303)	11,456
Deferred revenues	15,998	181,203	187,147
Accounts payable and accrued and other liabilities	111,939	(54,613)	55,235
Cash provided by operating activities	903,278	565,436	471,158
Investing activities:
Additions to property, equipment and leasehold improvements	(83,888)	(149,016)	(126,873)
Acquisitions - cash paid (net of cash acquired)	0	(25,989)	(15,855)
Divestitures - cash received (net of cash transferred)	0	0	526,779
Proceeds from the sale of an equity security	0	14,120	0
Cash (used in) provided by investing activities	(83,888)	(160,885)	384,051
Financing activities:
Proceeds from employee stock purchase plan	18,085	17,629	14,689
Proceeds from borrowings	2,000,000	5,000	0
Early redemption premium payment	(30,752)	0	0
Payments for deferred financing fees	(25,786)	0	0
Proceeds from revolving credit facility	332,000	309,000	248,000
Payments on revolving credit facility	(475,000)	(316,000)	(688,000)
Payments on borrowings	(2,058,469)	(102,579)	(570,972)
Purchases of treasury stock	(176,302)	(199,042)	(260,832)
Cash used in financing activities	(416,224)	(285,992)	(1,257,115)
Net increase (decrease) in cash and cash equivalents and restricted cash	403,166	118,559	(401,906)
Effects of exchange rates on cash and cash equivalents and restricted cash	28,581	3,614	(6,489)
Cash and cash equivalents and restricted cash, beginning of year	280,836	158,663	567,058
Cash and cash equivalents and restricted cash, end of year	712,583	280,836	158,663
Cash paid during the year for:
Interest	112,249	102,298	117,500
Income taxes, net of refunds received	$ 33,921	$ 119,156	$ 95,800