Condensed Consolidated Statements of Financial Condition - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Assets
Cash and cash equivalents	$ 456,116,000	$ 461,207,000
Cash segregated under regulatory requirements	5,751,000	3,199,000
Securities owned	32,767,000	32,361,000
Marketable securities	191,697,000	650,400,000
Receivables from broker-dealers, clearing organizations, customers and related broker-dealers	1,704,582,000	812,240,000
Accrued commissions receivable, net	367,425,000	342,299,000
Loans, forgivable loans and other receivables from employees and partners, net	228,008,000	158,176,000
Fixed assets, net	145,378,000	145,873,000
Investments	41,111,000	33,813,000
Goodwill	814,105,000	811,766,000
Other intangible assets, net	228,493,000	233,967,000
Receivables from related parties	23,257,000	15,466,000
Other assets	311,037,000	290,687,000
Total assets	4,549,727,000	3,991,454,000
Liabilities, Redeemable Partnership Interest, and Equity
Securities loaned	0	117,890,000
Accrued compensation	290,839,000	303,959,000
Securities sold, not yet purchased	1,834,000	0
Payables to broker-dealers, clearing organizations, customers and related broker-dealers	1,601,927,000	714,823,000
Payables to related parties	45,043,000	21,551,000
Accounts payable, accrued and other liabilities	546,533,000	692,639,000
Notes payable and collateralized borrowings	838,635,000	840,877,000
Total liabilities	$ 3,324,811,000	$ 2,691,739,000
Commitments and contingencies (Note 19)
Redeemable partnership interest	$ 55,449,000	$ 57,145,000
Stockholders' equity:
Additional paid-in capital	1,380,354,000	1,109,000,000
Treasury stock, at cost: 43,987 and 36,796 shares of Class A common stock at March 31, 2016 and December 31, 2015, respectively	(261,832,000)	(212,331,000)
Retained deficit	(297,816,000)	(273,492,000)
Accumulated other comprehensive income (loss)	(19,073,000)	(25,056,000)
Total stockholders' equity	854,703,000	651,123,000
Noncontrolling interest in subsidiaries	314,764,000	591,447,000
Total equity	1,169,467,000	1,242,570,000
Total liabilities, redeemable partnership and noncontrolling interests, and equity	4,549,727,000	3,991,454,000
Contingent Consideration Classified as Equity [Member]
Stockholders' equity:
Contingent Class A common stock	49,915,000	50,095,000
Class A Common Stock [Member]
Stockholders' equity:
Common stock value	2,807,000	2,559,000
Total equity	2,807,000	2,559,000
Class B Common Stock [Member]
Stockholders' equity:
Common stock value	348,000	348,000
Total equity	$ 348,000	$ 348,000