Receivables From And Payables To Brokers, Dealers And Clearing Organizations (Amounts Receivable From Brokers, Dealers, And Clearing Organizations) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Receivables From And Payables To Brokers, Dealers And Clearing Organizations [Abstract]
Deposits paid for securities borrowed	$ 173,434	$ 193,509
Receivable from clearing organizations	7,984	43,642
Securities failed to deliver	31,329	15,485
Receivables from brokers, dealers and clearing organizations, Total	$ 212,747	$ 252,636