Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 259,847	$ 393,692	$ 992,932
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization of property	31,498	33,264	32,785
Amortization of deferred expenses and share-based incentive compensation	359,381	341,825	320,472
Amortization and other acquisition-related costs	9,514	35,247	5,821
Deferred tax provision (benefit)	501,163	63,660	(1,100,785)
Provision (benefit) pursuant to tax receivable agreement	(202,546)		547,691
Loss on extinguishment of debt		3,148	60,219
Gain on acquisition of portion of business already owned		(12,668)
Gain on disposal of subsidiaries			(24,388)
(Increase) decrease in operating assets:
Deposits with banks and short-term investments	(430,388)	(44,278)	(207,373)
Cash deposited with clearing organizations and other segregated cash	(5,170)	5,767	6,909
Receivables-net	95,976	(156,129)	33,145
Investments	28,922	71,552	64,159
Other assets	(80,550)	(55,611)	(90,138)
Increase (decrease) in operating liabilities:
Deposits and other payables	428,826	(17,095)	225,008
Accrued compensation and benefits and other liabilities	18,969	(61,087)	20,839
Net cash provided by operating activities	1,015,442	601,287	887,296
CASH FLOWS FROM INVESTING ACTIVITIES:
Additions to property	(27,670)	(38,749)	(26,629)
Disposals of property	750	1,096	677
Net cash used in investing activities	(26,920)	(37,653)	(25,952)
Proceeds from:
Contributions from noncontrolling interests		93	275
Issuance of senior debt, net of expenses		296,757	396,272
Excess tax benefits from share-based incentive compensation		4,071	13,300
Other financing activities		24,484
Payments for:
Senior debt		(101,441)	(509,098)
Capital lease obligations	(7,337)	(1,619)	(1,826)
Distributions to noncontrolling interests	(5,193)	(2,111)	(16,296)
Payments under tax receivable agreement	(789)	(10,086)	(1,276)
Partial extinguishment of tax receivable agreement obligation			(42,222)
Purchase of Class A common stock	(306,741)	(300,217)	(172,772)
Class A common stock dividends	(341,450)	(336,138)	(290,684)
Settlement of vested share-based incentive compensation	(67,899)	(56,078)	(120,116)
Other financing activities	(10,984)	(4,667)	(2,361)
Net cash used in financing activities	(740,393)	(486,952)	(746,804)
EFFECT OF EXCHANGE RATE CHANGES ON CASH	76,922	(49,980)	(49,037)
NET INCREASE IN CASH AND CASH EQUIVALENTS	325,051	26,702	65,503
CASH AND CASH EQUIVALENTS—January 1	1,158,785	1,132,083	1,066,580
CASH AND CASH EQUIVALENTS—December 31	1,483,836	1,158,785	1,132,083
Cash paid during the year for:
Interest	49,601	46,262	45,359
Income taxes, net of refunds	$ 48,738	$ 72,420	$ 60,716