Receivables From And Payables To Brokers, Dealers And Clearing Organizations (Amounts Receivable From Brokers, Dealers, And Clearing Organizations) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Due To And From Broker Dealers And Clearing Organizations [Abstract]
Deposits paid for securities borrowed	$ 428,274	$ 318,105
Securities failed to deliver	60,777	23,649
Receivables from clearing organizations	59,419	260,077
Receivables from brokers, dealers and clearing organizations, Total	$ 548,470	$ 601,831