Counterparty Risk (% Of Total Receivable For Securities Sold) (Details)	Dec. 31, 2012
Royal Bank of Scotland [Member]
Financial Highlights [Line Items]
% of Total Receivable for Securities Sold	28.00%
Barclays Capital Inc. [Member]
Financial Highlights [Line Items]
% of Total Receivable for Securities Sold	24.00%
CS First Boston [Member]
Financial Highlights [Line Items]
% of Total Receivable for Securities Sold	21.00%