Condensed Consolidated Statements of Financial Condition (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents	$ 1,070,342	$ 388,409
Cash segregated under regulatory requirements	6,570	3,392
Reverse repurchase agreements	49,063
Securities owned	32,016	32,003
Receivables from broker-dealers, clearing organizations, customers and related broker-dealers	1,431,962	297,688
Accrued commissions receivable, net	263,897	222,299
Loans, forgivable loans and other receivables from employees and partners, net	124,798	220,098
Fixed assets, net	132,203	141,109
Investments	21,727	25,556
Goodwill	163,684	164,874
Other intangible assets, net	20,644	20,320
Receivables from related parties	12,408	21,655
Other assets	118,954	101,536
Total assets	3,448,268	1,638,939
Liabilities, Redeemable Partnership Interest, and Equity
Accrued compensation	273,870	125,793
Payables to broker-dealers, clearing organizations, customers and related broker-dealers	1,424,751	254,289
Payables to related parties	41,228	40,700
Accounts payable, accrued and other liabilities	446,619	260,462
Notes payable and collateralized borrowings	273,805	301,444
Notes payable to related parties	150,000	150,000
Total liabilities	2,610,273	1,132,688
Commitments and contingencies (Note 17)
Redeemable partnership interest	79,374	78,839
Stockholders' equity:
Additional paid-in capital	717,066	575,381
Contingent Class A common stock	15,791	18,868
Treasury stock, at cost: 18,075 and 18,041 shares of Class A common stock at June 30, 2013 and December 31, 2012, respectively	(110,219)	(110,090)
Retained deficit	(145,835)	(147,452)
Accumulated other comprehensive loss	(6,845)	(4,182)
Total stockholders' equity	471,850	334,292
Noncontrolling interest in subsidiaries	286,771	93,120
Total equity	758,621	427,412
Total liabilities, redeemable partnership interest, and equity	3,448,268	1,638,939
Class A Common Stock [Member]
Stockholders' equity:
Common stock value	1,544	1,419
Total equity	1,544	1,419
Class B Common Stock [Member]
Stockholders' equity:
Common stock value	348	348
Total equity	$ 348	$ 348