Receivables From And Payables To Brokers, Dealers And Clearing Organizations (Amounts Receivable From Brokers, Dealers, And Clearing Organizations) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Due To And From Broker Dealers And Clearing Organizations [Abstract]
Deposits paid for securities borrowed	$ 379,244	$ 318,105
Receivables from clearing organizations	78,635	260,077
Securities failed to deliver	75,385	23,649
Receivables from brokers, dealers and clearing organizations, Total	$ 533,264	$ 601,831