Derivatives Offsetting Liabilities (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability		$ 2,039	$ 269
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		2,039	269
Derivative, Collateral, Right to Reclaim Securities	[1]	(346)	(180)
Derivative, Collateral, Right to Reclaim Cash		(873)	0
Derivative Liability, Fair Value, Amount Offset Against Collateral		820	89
Interest rate swaps
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability		0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		0	0
Derivative, Collateral, Right to Reclaim Securities	[1]	0	0
Derivative, Collateral, Right to Reclaim Cash		0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral		0	0
TBA securities
Offsetting Liabilities [Line Items]
Derivative Liability, Fair Value, Gross Liability		2,039	269
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		2,039	269
Derivative, Collateral, Right to Reclaim Securities	[1]	(346)	(180)
Derivative, Collateral, Right to Reclaim Cash		(873)	0
Derivative Liability, Fair Value, Amount Offset Against Collateral		$ 820	$ 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.