Eurodollar Futures Positions (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	1.84%
Open Equity	$ 6,392,000
Cash Held by Broker as Margin on Eurodollar Futures Contracts	2,531,000	0
[Year2013ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	0.34%
Notional Amount	250,000,000
Open Equity	(7,000)
[Year2014ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	0.54%
Notional Amount	250,000,000
Open Equity	173,000
[Year2015ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	1.15%
Notional Amount	250,000,000
Open Equity	890,000
[Year2016ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	2.15%
Notional Amount	250,000,000
Open Equity	1,989,000
[Year2017ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	3.00%
Notional Amount	250,000,000
Open Equity	2,219,000
[Year2018ExpirationMember]
Eurodollar Futures [Line Items]
Locked-In LIBOR Rate	3.54%
Notional Amount	250,000,000
Open Equity	$ 1,128,000