Derivative Financial Instruments - Summary of Eurodollar Futures Positions (Details) (Eurodollar Future [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Locked-In LIBOR Rate	1.37%	1.73%
Notional Amount	$ 835,714,000	$ 760,000,000
Open Equity	(15,263,000)	(4,302,000)
Year 2015 Expiration [Member]
Derivatives, Fair Value [Line Items]
Locked-In LIBOR Rate	0.51%	0.63%
Notional Amount	800,000,000	650,000,000
Open Equity	(1,791,000)	(1,039,000)
Year 2016 Expiration [Member]
Derivatives, Fair Value [Line Items]
Locked-In LIBOR Rate	1.13%	1.54%
Notional Amount	900,000,000	800,000,000
Open Equity	(3,435,000)	139,000
Year 2017 Expiration [Member]
Derivatives, Fair Value [Line Items]
Locked-In LIBOR Rate	1.74%	2.23%
Notional Amount	825,000,000	800,000,000
Open Equity	(4,976,000)	(1,041,000)
Year 2018 Expiration [Member]
Derivatives, Fair Value [Line Items]
Locked-In LIBOR Rate	2.09%	2.54%
Notional Amount	800,000,000	800,000,000
Open Equity	$ (5,061,000)	$ (2,361,000)