Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Consolidated net income (loss)	$ 84,943	$ 279,866	$ 81,729
Less: Consolidated net income from discontinued operations, net of tax		(176,169)	(170,365)
Adjustments to reconcile consolidated net income (loss) to net cash provided by (used in) operating activities:
Fixed asset depreciation and intangible asset amortization	79,466	71,495	65,444
Employee loan amortization and reserves on employee loans	35,650	13,015	26,930
Equity-based compensation and allocations of net income to limited partnership units and FPUs	165,612	205,070	233,241
Deferred compensation expense	5,879	5,879	7,986
Losses (gains) on equity method investments	(4,115)	(7,377)	(4,627)
Realized losses (gains) on marketable securities	(3,528)	(11,831)	(60)
Unrealized losses (gains) on marketable securities	(3,204)	2,316	(23,936)
Loss (gains) on other investments	(22,785)	(38,491)
Amortization of discount (premium) on notes payable	3,223	(1,081)	843
Impairment of fixed assets, intangible assets and investments	4,466	2,807	5,074
Deferred tax provision (benefit)	(1,803)	(22,635)	19,858
Change in estimated acquisition earn-out payables	5,622	2,885	5,003
Forfeitures of Class A common stock	(139)	(1,458)	(1,153)
Other	(5,682)		(557)
Consolidated net income (loss) adjusted for non-cash and non-operating items	343,605	324,291	245,410
Decrease (increase) in operating assets:
Reverse repurchase agreements		986	54,659
Securities owned	883	(25,401)	2,350
Receivables from broker-dealers, clearing organizations, customers and related broker-dealers	389,058	(206,051)	(239,230)
Accrued commissions receivable, net	(12,418)	(108,851)	(35,617)
Loans, forgivable loans and other receivables from employees and partners, net	(119,469)	(104,266)	(64,846)
Receivables from related parties	(4,215)	37,506	128,192
Other assets	3,784	(30,924)	2,189
Increase (decrease) in operating liabilities:
Repurchase agreements	(986)
Securities loaned	(1,238)	(129,580)	144,720
Accrued compensation	(4,131)	(52,953)	(92,027)
Payables to broker-dealers, clearing organizations, customers and related broker-dealers	(353,313)	165,517	225,763
Payables to related parties	32,342	(833)	10,513
Accounts payable, accrued and other liabilities	(34,840)	63,214	10,684
Net cash provided by (used in) operating activities	239,062	(67,345)	392,760
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of fixed assets	(46,665)	(24,528)	(25,039)
Capitalization of software development costs	(48,846)	(49,813)	(33,226)
Purchase of equity method investments	(1,715)	(925)	(106,824)
Proceeds from equity method investments	3,737	7,046	243
Payments for acquisitions, net of cash acquired	28,261	(50,562)	13,697
Proceeds from sale of marketable securities	24,626	128,018	38,256
Capitalization of trademarks, patent defense and registration costs			329
Net cash provided by (used in) investing activities	(40,602)	9,236	(112,564)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayments of long-term debt and collateralized borrowings	(332,378)	(449,598)	(10,629)
Issuance of long-term debt and collateralized borrowings, net of deferred issuance costs	709,849	639,196	1,001,508
Earnings distributions to limited partnership interests and other noncontrolling interests	(113,673)	(163,935)	(126,243)
Redemption and repurchase of limited partnership interests	(43,270)	(51,943)	(45,593)
Dividends to stockholders	(192,442)	(231,446)	(200,116)
Repurchase of Class A common stock	(1,236)	(10,439)	(16,773)
Cancellation of restricted stock units in satisfaction of withholding tax requirements	(458)	(647)	(865)
Proceeds from issuance of Class A common stock, net of costs		327,624	26,606
Acquisition of Berkeley Point			(871,816)
Proceeds from exercise of stock options			72
Proceeds from short-term borrowings			6,046
Payments on acquisition earn-outs	(8,146)	(7,924)
Net cash provided by (used in) financing activities	18,246	50,888	(237,803)
Net cash provided by (used in) operating activities from discontinued operations	0	(748,231)	895,853
Net cash provided by (used in) investing activities from discontinued operations	0	18,347	(41,027)
Net cash provided by (used in) financing activities from discontinued operations	0	367,931	(697,275)
Effect of exchange rate changes on Cash and cash equivalents, Restricted cash and Cash segregated under regulatory requirements	2,630	(10,838)	3,411
Net increase (decrease) in Cash and cash equivalents, and Cash segregated under regulatory requirements	219,336	(380,012)	203,355
Cash and cash equivalents, and Cash segregated under regulatory requirements at beginning of period	416,778	796,790	593,435
Cash and cash equivalents, and Cash segregated under regulatory requirements at end of period	636,114	416,778	796,790
Supplemental cash information:
Cash paid during the period for taxes	47,997	66,540	78,300
Cash paid during the period for interest	51,776	41,951	75,305
Supplemental non-cash information:
Issuance of Class A common stock upon exchange of limited partnership interests	26,146	143,232	106,698
Issuance of Class A and contingent Class A common stock and limited partnership interests for acquisitions	3,040	$ 21,899	14,232
Right-of-use assets and liabilities	$ 169,065
Nasdaq [Member]
Supplemental non-cash information:
Value of shares received for Nasdaq earn-out			$ 76,969