Eurodollar Futures Positions (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	1.95%
Open Equity	$ 4,167,000
Cash Held by Broker as Margin on Eurodollar Futures Contracts	2,581,000	0
[Year2014ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	0.47%
Notional Amount	262,500,000
Open Equity	(96,000)
[Year2015ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	0.89%
Notional Amount	275,000,000
Open Equity	95,000
[Year2016ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	1.86%
Notional Amount	250,000,000
Open Equity	1,286,000
[Year2017ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	2.83%
Notional Amount	250,000,000
Open Equity	1,794,000
[Year2018ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	3.51%
Notional Amount	250,000,000
Open Equity	$ 1,088,000