Derivative Financial Instruments (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Not Designated as Hedging Instruments [Member]
DERIVATIVE FINANCIAL INSTRUMENTS-STATEMENT OF OPERATIONS INFORMATION
Derivative financial instruments, net gain (loss) recognized	$ 121	$ (9,099)	$ 219	$ (8,191)
Revenues - principal transactions and other income [Member] | Foreign currency forward contracts [Member]
DERIVATIVE FINANCIAL INSTRUMENTS-STATEMENT OF OPERATIONS INFORMATION
Derivative financial instruments, net gain (loss) recognized	(35)
Revenues - principal transactions and other income [Member] | Not Designated as Hedging Instruments [Member] | Foreign currency forward contracts [Member]
DERIVATIVE FINANCIAL INSTRUMENTS-STATEMENT OF OPERATIONS INFORMATION
Derivative financial instruments, net gain (loss) recognized		(922)	(35)	(219)
Revenues - net trading [Member] | Not Designated as Hedging Instruments [Member] | EuroDollar futures contracts [Member]
DERIVATIVE FINANCIAL INSTRUMENTS-STATEMENT OF OPERATIONS INFORMATION
Derivative financial instruments, net gain (loss) recognized		(64)	0	(2)
Revenues - net trading [Member] | Not Designated as Hedging Instruments [Member] | TBAs [Member]
DERIVATIVE FINANCIAL INSTRUMENTS-STATEMENT OF OPERATIONS INFORMATION
Derivative financial instruments, net gain (loss) recognized	$ 154	$ (8,113)	$ 254	$ (7,970)