Significant Accounting Policies - Cash and Cash Equivalents (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Abstract]
Cash Held by Broker as Margin on Eurodollar Futures Contracts	$ 2,031,000	$ 0
Cash Held on Deposit with Repurchase Agreement Counterparties	0	449,000
Commentary - Cash and Cash Equivalents Balances That Are Insured by the FDIC	The Company maintains cash balances at two banks, and, at times, balances may exceed federally insured limits. The Company has not experienced any losses related to these balances. All non-interest bearing cash balances were fully insured at December 31, 2012 due to a temporary federal program in effect from December 31, 2010 through December 31, 2012. Under the program, there was no limit to the amount of insurance for eligible accounts. Beginning January 1, 2013, insurance reverted to $250,000 per depositor at each financial institution. At March 31, 2013, the Company’s cash deposits exceeded federally insured limits by $2.3 million. Restricted cash balances are uninsured, but are held in separate customer accounts that are segregated from the general funds of the counterparty. The Company believes that it is not exposed to any significant credit risk on cash and cash equivalents or restricted cash balances.
CashUninsuredAmount	$ 2,300,000