OTHER ASSETS AND ACCOUNTS PAYABLE, ACCRUED EXPENSES AND OTHER LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Other assets
Interest and Notes Receivable	$ 424,972		$ 469,456
Due from Broker	240,858		189,202
Intangible Assets, net	192,499		197,484
Deferred Tax Assets, net	122,002		105,654
Unsettled Investment Sales	108,689		90,666
Goodwill	89,000		89,000
Fixed Assets, net	78,322		79,570
Receivables	46,059		267,126
Deferred Financing Costs	26,100		20,918
Deferred Transaction Costs	16,781		14,633
Prepaid Expenses	16,183		12,079
Refundable Security Deposits	7,340		7,428
Other	25,805		15,061
Total Other Assets	1,618,238		1,701,055
Interest rate on promissory notes, low end of range (as a percent)	1.50%
Interest rate on promissory notes, high end of range (as a percent)	3.00%
Intangible assets, accumulated amortization	26,387		21,402
Intangible assets, amortization expense	4,985	947
Accumulated depreciation and amortization	95,683		92,467
Depreciation and amortization expense	3,697	2,572
Foreign currency contract cost basis	2,332		2,332
Accounts Payable, Accrued Expenses and Other Liabilities
Amounts Payable to Carry Pool	900,158		776,750
Securities Sold Short	426,754		350,353
Unsettled Investment Purchases	212,905		172,583
Accounts Payable and Accrued Expenses	152,622		97,389
Contingent Consideration Obligation	81,600		71,300
Due to Broker	77,865		49,204
Accrued Compensation and Benefits	51,900		17,265
Deferred Rent and Income	25,649		19,228
Interest Payable	9,896		11,746
Taxes Payable	5,602		9,250
Other Liabilities	6,607		16,911
Total accounts payable, accrued expenses and other liabilities	2,052,607		1,824,655
Securities sold, not yet purchased, cost basis	409,070		343,440
Cost basis for instruments	36,629,676		36,647,369
Foreign Exchange Contracts
Other assets
Foreign currency contract assets	215,082		137,786
Accounts Payable, Accrued Expenses and Other Liabilities
Foreign currency contract liabilities	99,739		229,314
Foreign Exchange Options
Other assets
Foreign currency contract assets	8,546		4,992
Accounts Payable, Accrued Expenses and Other Liabilities
Foreign currency contract liabilities	1,310		3,362
Cost basis for instruments	$ 0		$ 0