Derivative Financial Instruments - Summary of TBA Contracts (Details) - Thirty Year [Member]	Dec. 31, 2016 USD ($)
Derivatives, Fair Value [Line Items]
Notional Amount	$ (200,000,000)
Cost Basis	(203,304,000)
Market Value Of To Be Announced Contracts	(204,422,000)
Assets, at Fair Value	(1,118,000)
Three Percent [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	(100,000,000)
Cost Basis	(99,406,000)
Market Value Of To Be Announced Contracts	(99,344,000)
Assets, at Fair Value	62,000
Four Percent [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	(100,000,000)
Cost Basis	(103,898,000)
Market Value Of To Be Announced Contracts	(105,078,000)
Assets, at Fair Value	$ (1,180,000)