Derivatives Offsetting Assets (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 4,754	$ 2,940
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		4,754	2,940
Derivative, Collateral, Obligation to Return Securities	[1]	0	(180)
Derivative, Collateral, Obligation to Return Cash		1,674	666
Derivative Asset, Fair Value, Amount Offset Against Collateral		3,080	2,094
Interest rate swaps
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		1,081	791
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		1,081	791
Derivative, Collateral, Obligation to Return Securities	[1]	0	0
Derivative, Collateral, Obligation to Return Cash		0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral		1,081	791
Eurodollar futures
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		1,674	666
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		1,674	666
Derivative, Collateral, Obligation to Return Securities	[1]	0	0
Derivative, Collateral, Obligation to Return Cash		(1,674)	(666)
Derivative Asset, Fair Value, Amount Offset Against Collateral		0	0
TBA securities
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		1,999	1,483
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		1,999	1,483
Derivative, Collateral, Obligation to Return Securities	[1]	0	(180)
Derivative, Collateral, Obligation to Return Cash		0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral		$ 1,999	$ 1,303

[1] Amounts disclosed for collateral received by or posted to the same counterparty include cash and the fair value of MBS up to and not exceeding the net amount of the asset or liability presented in the balance sheet. The fair value of the total collateral received by or posted to the same counterparty may exceed the amounts presented.