Receivables from and Payables to Brokers, Dealers, and Clearing Agencies (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Receivables from and Payables to Brokers, Dealers, and Clearing Agencies (Textual) [Abstract]
Interest on margin payable	$ 415	$ 358	$ 831	$ 983