Derivative Financial Instruments - Summary of TBA Contracts - 30 Year [Member] - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional Amount	$ (400,000,000)	$ (200,000,000)
Cost Basis	(412,594,000)	(203,304,000)
Market Value Of TBA Contract	(410,504,000)	(204,422,000)
Assets, at Fair Value	2,090,000
Liabilities, at Fair Value		(1,118,000)
3% [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	(250,000,000)	(100,000,000)
Cost Basis	(251,063,000)	(99,406,000)
Market Value Of TBA Contract	(249,628,000)	(99,344,000)
Assets, at Fair Value	1,435,000	62,000
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	(150,000,000)
Cost Basis	(161,531,000)
Market Value Of TBA Contract	(160,876,000)
Assets, at Fair Value	$ 655,000