Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Consolidated net income (loss)	$ 111,499	$ 309,725
Less: Consolidated net income from discontinued operations, net of tax		(165,128)
Adjustments to reconcile consolidated net income (loss) to net cash provided by (used in) operating activities:
Fixed asset depreciation and intangible asset amortization	58,710	51,944
Employee loan amortization and reserves on employee loans	23,286	3,009
Equity-based compensation and allocations of net income to limited partnership units and FPUs	96,223	119,892
Deferred compensation expense	1,193	3,766
Losses (gains) on equity method investments	(3,051)	(4,962)
Realized losses (gains) on marketable securities	(3,528)	(11,213)
Unrealized losses (gains) on marketable securities	(2,197)	932
Unrealized losses (gains) on other investments	(20,396)	(38,344)
Amortization of discount (premium) on notes payable	2,216	(1,600)
Impairment of fixed assets, intangible assets and investments	1,302	2,271
Deferred tax provision (benefit)	181	5,388
Change in estimated acquisition earn-out payables	(4,371)	(1,594)
Forfeitures of Class A common stock	(139)	(1,219)
Consolidated net income (loss), adjusted for non-cash and non-operating items	260,928	272,867
Decrease (increase) in operating assets:
Securities owned	(1,990)	(42,904)
Receivables from broker-dealers, clearing organizations, customers and related broker-dealers	(2,529,636)	(1,942,941)
Accrued commissions receivable, net	15,115	(99,320)
Loans, forgivable loans and other receivables from employees and partners, net	(76,489)	(75,535)
Receivables from related parties	91	(330,490)
Other assets	(15,158)	(21,603)
Increase (decrease) in operating liabilities:
Repurchase agreements	909	198
Securities loaned	(2,140)	(86,982)
Accrued compensation	(5,583)	(33,070)
Payables to broker-dealers, clearing organizations, customers and related broker-dealers	2,529,655	1,888,760
Payables to related parties	45,047	(6,889)
Accounts payable, accrued and other liabilities	(87,169)	398
Net cash provided by (used in) operating activities	133,580	(477,511)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of fixed assets	(36,618)	(19,757)
Capitalization of software development costs	(29,997)	(34,140)
Purchase of equity method investments	(1,103)	(599)
Proceeds from equity method investments	3,737	7,046
Investment in memberships		(642)
Payments for acquisitions, net of cash and restricted cash acquired	26,264	(1,366)
Proceeds from sale of marketable securities	24,626	102,076
Net cash provided by (used in) investing activities	(13,091)	52,618
CASH FLOWS FROM FINANCING ACTIVITIES:
Repayments of long-term debt and collateralized borrowings	(328,974)	(320,900)
Issuance of long-term debt and collateralized borrowings, net of deferred issuance costs	670,263	639,241
Earnings distributions to limited partnership interests and other noncontrolling interests	(74,484)	(117,729)
Redemption and repurchase of limited partnership interests	(22,736)	(11,432)
Dividends to stockholders	(131,039)	(172,029)
Repurchase of Class A common stock	(1,236)	(9,806)
Cancellation of restricted stock units in satisfaction of withholding tax requirements	(458)	(647)
Proceeds from issuance of Class A common stock, net of costs		327,624
Loan from related parties, net of repayments		80,000
Payments on acquisition earn-outs	(7,888)	(7,924)
Net cash provided by (used in) financing activities	103,448	406,398
Net cash provided by (used in) operating activities from discontinued operations	0	(280,543)
Net cash provided by (used in) investing activities from discontinued operations	0	(12,242)
Net cash provided by (used in) financing activities from discontinued operations	0	(89,319)
Effect of exchange rate changes on Cash and cash equivalents, Restricted cash and Cash segregated under regulatory requirements	(3,235)	(7,831)
Net (decrease) increase in Cash and cash equivalents, Restricted cash and Cash segregated under regulatory requirements	220,702	(408,430)
Cash and cash equivalents, Restricted cash and Cash segregated under regulatory requirements at beginning of period	416,778	796,790
Cash and cash equivalents, Restricted cash and Cash segregated under regulatory requirements at end of period	637,480	388,360
Supplemental cash information:
Cash paid during the period for taxes	28,817	37,534
Cash paid during the period for interest	41,830	32,141
Supplemental non-cash information:
Issuance of Class A common stock upon exchange of limited partnership interests	23,414	127,322
Issuance of Class A and contingent Class A common stock and limited partnership interests for acquisitions	$ 3,038	$ 19,732