Condensed Consolidated Statements of Financial Condition - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 462,042,000	$ 502,024,000
Cash segregated under regulatory requirements	119,470,000	6,895,000
Reverse repurchase agreements	0	54,659,000
Securities owned	33,743,000	35,357,000
Marketable securities	169,241,000	164,820,000
Receivables from broker-dealers, clearing organizations, customers and related broker-dealers	1,647,686,000	497,557,000
Accrued commissions receivable, net	576,595,000	374,734,000
Loans, forgivable loans and other receivables from employees and partners, net	299,595,000	267,527,000
Loan receivables from related parties	150,000,000
Fixed assets, net	175,737,000	165,867,000
Investments	35,122,000	33,439,000
Goodwill	884,753,000	863,690,000
Other intangible assets, net	316,049,000	247,723,000
Receivables from related parties	8,970,000	6,967,000
Other assets	301,879,000	287,141,000
Total assets	5,180,882,000	3,508,400,000
Liabilities, Redeemable Partnership Interest, and Equity
Short-term borrowings	150,000,000
Securities loaned	95,327,000	0
Accrued compensation	345,425,000	333,144,000
Payables to broker-dealers, clearing organizations, customers and related broker-dealers	1,488,148,000	375,152,000
Payables to related parties	39,349,000	28,976,000
Accounts payable, accrued and other liabilities	900,841,000	599,046,000
Notes payable and collateralized borrowings	990,887,000	965,767,000
Total liabilities	4,009,977,000	2,302,085,000
Commitments and contingencies (Note 18)
Redeemable partnership interest	51,475,000	52,577,000
Stockholders’ equity:
Additional paid-in capital	1,520,627,000	1,466,586,000
Treasury stock, at cost: 48,665 and 47,679 shares of Class A common stock at June 30, 2017 and December 31, 2016, respectively	(297,378,000)	(288,743,000)
Retained deficit	(415,053,000)	(358,526,000)
Accumulated other comprehensive income (loss)	(13,001,000)	(23,199,000)
Total stockholders’ equity	836,856,000	841,863,000
Noncontrolling interest in subsidiaries	282,574,000	311,875,000
Total equity	1,119,430,000	1,153,738,000
Total liabilities, redeemable partnership interest, and equity	5,180,882,000	3,508,400,000
Contingent Consideration Classified as Equity [Member]
Stockholders’ equity:
Contingent Class A common stock	38,316,000	42,472,000
Class A Common Stock [Member]
Stockholders’ equity:
Common stock value	2,997,000	2,925,000
Total equity	2,997,000	2,925,000
Class B Common Stock [Member]
Stockholders’ equity:
Common stock value	348,000	348,000
Total equity	$ 348,000	$ 348,000