Investment in Securities (Summary of Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Securities, Available-for-sale [Line Items]
Interest Income	$ 40,146	$ 43,075	$ 126,115	$ 134,463
Agency RMBS
Securities, Available-for-sale [Line Items]
Coupon Interest	14,797	14,117	43,449	47,632
Net Amortization	(9,551)	(7,454)	(20,123)	(25,516)
Interest Income	5,246	6,663	23,326	22,116
Non-Agency RMBS and CMBS
Securities, Available-for-sale [Line Items]
Coupon Interest	3,307	3,311	10,321	10,995
Net Amortization	748	1,911	3,179	4,001
Interest Income	4,055	5,222	13,500	14,996
CLOs
Securities, Available-for-sale [Line Items]
Coupon Interest	3,532	2,256	7,978	11,662
Net Amortization	(1,456)	2,179	59	1,543
Interest Income	2,076	4,435	8,037	13,205
Other Securities
Securities, Available-for-sale [Line Items]
Coupon Interest	4,590	2,970	12,296	8,992
Net Amortization	(1,813)	(1,435)	(3,796)	(3,584)
Interest Income	2,777	1,535	8,500	5,408
Securities Investment [Member]
Securities, Available-for-sale [Line Items]
Coupon Interest	26,226	22,654	74,044	79,281
Net Amortization	(12,072)	(4,799)	(20,681)	(23,556)
Interest Income	$ 14,154	$ 17,855	$ 53,363	$ 55,725