Receivables From And Payables To Brokers, Dealers And Clearing Organizations (Amounts Receivable From Brokers, Dealers, And Clearing Organizations) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Due To And From Broker Dealers And Clearing Organizations [Abstract]
Deposits paid for securities borrowed	$ 333,348	$ 445,542
Receivables from clearing organizations	295,856	198,079
Securities failed to deliver	22,070	7,453
Receivables from brokers, dealers and clearing organizations, Total	$ 651,274	$ 651,074