Derivatives Offsetting Liabilities (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability		$ 269	$ 6,922
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		269	6,922
Derivative, Collateral, Right to Reclaim Securities	[1]	(180)	(6,913)
Derivative, Collateral, Right to Reclaim Cash		0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral		89	9
Interest rate swaps
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability		0	6,922
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		0	6,922
Derivative, Collateral, Right to Reclaim Securities	[1]	0	(6,913)
Derivative, Collateral, Right to Reclaim Cash		0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral		0	$ 9
TBA securities
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability		269
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		269
Derivative, Collateral, Right to Reclaim Securities	[1]	(180)
Derivative, Collateral, Right to Reclaim Cash		0
Derivative Liability, Fair Value, Amount Offset Against Collateral		$ 89

[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.