DUE TO PRIME BROKERS (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Other Payables to Broker-Dealers and Clearing Organizations	$ 365,007	$ 260,359
Maximum temporary leverage	20.00%
Maximum long-term leverage	5.00%
Collateral for LOCs issued [Member]
Other Payables to Broker-Dealers and Clearing Organizations	238,100	256,100
Bank Overdrafts [Member]
Other Payables to Broker-Dealers and Clearing Organizations	$ 126,900	$ 4,300