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	Dec. 31, 2014	Dec. 31, 2013
Receivables From And Payables To Brokers, Dealers And Clearing Organizations [Abstract]
Deposits paid for securities borrowed	$ 445,542	$ 227,640
Receivable from clearing organizations	198,079	125,538
Securities failed to deliver	7,453	27,944
Receivables from brokers, dealers and clearing organizations, Total	$ 651,074	$ 381,122