Investment in Securities (Summary of Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Securities, Available-for-sale [Line Items]
Net Amortization									$ 32,578	$ 41,681	$ 48,132
Interest Income	$ 49,390	$ 40,146	$ 45,890	$ 40,079	$ 39,067	$ 43,075	$ 39,281	$ 52,108	175,505	173,531	159,901
Level 3
Securities, Available-for-sale [Line Items]
Assets, Transfers into Level 3									13,797	92,143	35,567
Agency RMBS
Securities, Available-for-sale [Line Items]
Coupon Interest									58,495	59,987	62,103
Net Amortization									(24,642)	(31,975)	(24,731)
Interest Income									33,853	28,012	37,372
Non-Agency RMBS and CMBS
Securities, Available-for-sale [Line Items]
Coupon Interest									13,987	15,257	13,855
Net Amortization									3,423	5,775	2,782
Interest Income									17,410	21,032	16,637
CLOs
Securities, Available-for-sale [Line Items]
Coupon Interest									10,701	14,103	15,857
Net Amortization									(1,035)	3,529	(1,599)
Interest Income									9,666	17,632	14,258
Other Securities
Securities, Available-for-sale [Line Items]
Coupon Interest									17,332	11,545	7,157
Net Amortization									(5,538)	(4,986)	(2,468)
Interest Income									11,794	6,559	4,689
Securities Investment [Member]
Securities, Available-for-sale [Line Items]
Coupon Interest									100,515	100,892	98,972
Net Amortization									(27,792)	(27,657)	(26,016)
Interest Income									$ 72,723	$ 73,235	$ 72,956