Derivative Financial Instruments - Summary of TBA Contracts - 30 Year [Member] - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional Amount	$ (447,000,000)	$ (200,000,000)
Cost Basis	(464,605,000)	(203,304,000)
Market Value Of TBA Contract	(466,841,000)	(204,422,000)
Liabilities, at Fair Value	(2,236,000)	(1,118,000)
3% [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	(150,000,000)	(100,000,000)
Cost Basis	(147,406,000)	(99,406,000)
Market Value Of TBA Contract	(148,781,000)	(99,344,000)
Assets, at Fair Value		62,000
Liabilities, at Fair Value	(1,375,000)
4.0% [Member]
Derivatives, Fair Value [Line Items]
Notional Amount		(100,000,000)
Cost Basis		(103,898,000)
Market Value Of TBA Contract		(105,078,000)
Liabilities, at Fair Value		$ (1,180,000)
4.5% [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	(297,000,000)
Cost Basis	(317,199,000)
Market Value Of TBA Contract	(318,060,000)
Liabilities, at Fair Value	$ (861,000)