Offsetting Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Offsetting of Derivative Assets
Gross Amounts	$ 13,776	$ 14,466
Derivative Asset	13,776	14,466
Net Amounts of Assets presented in the Consolidated Balance Sheets	5,111	2,606
Financial Instruments	(11,241)	(13,917)
Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	2,535	549
Gross amounts of derivative liability, fair value, gross liability	6,370	10,130
Derivative liabilities, net amounts of assets presented in consolidated balance sheets	6,370	10,130
Financial instruments, derivative liability, at fair value	(2,576)	(2,057)
Cash collateral, derivative liability, at fair value	(2,819)	(8,073)
Net Amount	975	0
Gross amounts of repurchase agreements	2,824,801	2,818,837
Repurchase agreement, net amounts of assets presented in consolidated balance sheets	2,824,801	2,818,837
Financial instruments, repurchase agreements	(2,824,801)	(2,818,837)
Gross amounts of derivative liability	2,831,171	2,828,967
Derivative liability, net amounts of assets presented in consolidated balance sheets	2,831,171	2,828,967
Derivative liability, financial instruments	(2,827,377)	(2,820,894)
Derivative liability, net amount	975	0
Derivative liability, cash collateral pledged	55,400	38,000
Fair value of investments pledged against repurchase agreements	3,200,000	3,300,000
Agency RMBS Interest-Only Strips accounted for as derivatives, included in MBS
Offsetting of Derivative Assets
Gross Amounts	8,665	11,860
Derivative Asset	8,665	11,860
Financial Instruments	(8,665)	(11,860)
Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	0	0
Derivative asset
Offsetting of Derivative Assets
Gross Amounts	5,111	2,606
Net Amounts of Assets presented in the Consolidated Balance Sheets	5,111	2,606
Financial Instruments	(2,576)	(2,057)
Derivative Asset, Fair Value, Offset Against Collateral, Net of Not Subject to Master Netting Arrangement, Policy Election	$ 2,535	$ 549