Investments in RMBS, Assets by Maturity (Details) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2022 USD ($) Security	Dec. 31, 2021 USD ($) Security
RMBS, Assets by Maturity [Abstract]
Carrying value		$ 774,113	$ 953,496
RMBS [Member]
RMBS, Assets by Maturity [Abstract]
Original face value		1,100,572	1,257,086
Book value		811,003	945,851
Gross unrealized gains		1,052	14,536
Gross unrealized losses		(37,942)	(6,891)
Carrying value	[1]	$ 774,113	$ 953,496
Number of securities | Security		110	121
Weighted average coupon		3.09%	3.06%
Weighted average yield	[2]	2.98%	2.93%
Weighted average maturity		28 years	28 years
RMBS [Member] | Over 10 Years [Member]
RMBS, Assets by Maturity [Abstract]
Original face value		$ 1,100,572	$ 1,257,086
Book value		811,003	945,851
Gross unrealized gains		1,052	14,536
Gross unrealized losses		(37,942)	(6,891)
Carrying value	[1],[3]	$ 774,113	$ 953,496
Number of securities | Security		110	121
Weighted average coupon		3.09%	3.06%
Weighted average yield	[2]	2.98%	2.93%
Weighted average maturity		28 years	28 years

[1] See Note 9 regarding the estimation of fair value, which approximates carrying value for all securities.

[2] The weighted average yield is based on the most recent gross monthly interest income, which is then annualized and divided by the book value of settled securities.

[3] The Company used an implied AAA rating for the Agency RMBS.