Derivatives Offsetting Assets (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 4,290	$ 6,563
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		4,290	6,563
Derivative, Collateral, Obligation to Return Securities	[1]	(380)	0
Derivative, Collateral, Obligation to Return Cash		0	1,719	[1]
Derivative Asset, Fair Value, Amount Offset Against Collateral		3,910	4,844
Interest rate swaption
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		573
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		573
Derivative, Collateral, Obligation to Return Securities	[1]	0
Derivative, Collateral, Obligation to Return Cash		0
Derivative Asset, Fair Value, Amount Offset Against Collateral		573
Options on U.S. Treasury futures
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		2,883
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		2,883
Derivative, Collateral, Obligation to Return Securities	[1]	0
Derivative, Collateral, Obligation to Return Cash		0
Derivative Asset, Fair Value, Amount Offset Against Collateral		2,883
Interest rate swaps
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset			324
Derivative Asset, Fair Value, Amount Not Offset Against Collateral			324
Derivative, Collateral, Obligation to Return Securities	[1]		0
Derivative, Collateral, Obligation to Return Cash			0
Derivative Asset, Fair Value, Amount Offset Against Collateral			324
Long position | TBA securities
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		834	6,239
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		834	6,239
Derivative, Collateral, Obligation to Return Securities	[1]	(380)	0
Derivative, Collateral, Obligation to Return Cash		0	(1,719)	[1]
Derivative Asset, Fair Value, Amount Offset Against Collateral		$ 454	$ 4,520

[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 derivative 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. Please refer to the consolidated balance sheets for the total cash posted as collateral, which is recorded as "restricted cash", and the total fair value of financial instruments pledged as collateral for derivatives and repurchase agreements, which is shown parenthetically.