Derivatives Offsetting Assets (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		$ 6,563	$ 2,940
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		6,563	2,940
Derivative, Collateral, Obligation to Return Securities	[1]	0	(180)
Derivative, Collateral, Obligation to Return Cash		1,719	666
Derivative Asset, Fair Value, Amount Offset Against Collateral		4,844	2,094
Interest rate swaps
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		324	791
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		324	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		324	791
Eurodollar futures
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset			666
Derivative Asset, Fair Value, Amount Not Offset Against Collateral			666
Derivative, Collateral, Obligation to Return Securities	[1]		0
Derivative, Collateral, Obligation to Return Cash			(666)
Derivative Asset, Fair Value, Amount Offset Against Collateral			0
TBA securities
Offsetting Assets [Line Items]
Derivative Asset, Fair Value, Gross Asset		6,239	1,483
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		6,239	1,483
Derivative, Collateral, Obligation to Return Securities	[1]	0	(180)
Derivative, Collateral, Obligation to Return Cash		(1,719)	0
Derivative Asset, Fair Value, Amount Offset Against Collateral		$ 4,520	$ 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 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.