Derivative Financial Instruments - Income Statement Effect (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	$ (13,925,000)	$ 4,828,000	$ (40,000)
Eurodollar Future [Member]
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	(9,558,000)	4,828,000	(39,725)
Interest Rate Swaption [Member]
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	(4,439,000)	0	0
Treasury Note Future [Member]
Derivatives, Fair Value [Line Items]
(Losses) gains on derivative instruments	$ 72,000	$ 0	$ 0