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, 2011	Sep. 30, 2011	Dec. 31, 2010
Deposits paid for securities borrowed	$ 193,509		$ 94,709
Securities failed to deliver	15,485		74,991
Receivable from clearing organizations	43,642		78,007
Receivables from brokers, dealers and clearing organizations, Total	252,636
Trading securities pledged	$ 392,395	$ 392,400