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, 2013	Dec. 31, 2012
Receivables From And Payables To Brokers, Dealers And Clearing Organizations [Abstract]
Deposits paid for securities borrowed	$ 331,784	$ 153,819
Receivable from clearing organizations	206,321	115,996
Securities failed to deliver	9,531	6,409
Receivables from brokers, dealers and clearing organizations, Total	$ 547,636	$ 276,224