Investment in Securities (Proceeds, Realized Gains (Losses) on Sales) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Securities, Available-for-sale [Line Items]
Proceeds	$ 328,763,000	$ 40,462,000	$ 1,116,415,000	$ 1,765,704,000
Available-for-sale Securities, Gross Realized Gains	10,024,000	4,509,000	24,154,000	29,458,000
Available-for-sale Securities, Gross Realized Losses	(3,254,000)	(553,000)	(12,870,000)	(10,506,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	6,770,000	3,956,000	11,284,000	18,952,000
Available-for-sale securities Realizes Losses - adjustments to cost basis of certain securities	(300,000)	(2,500,000)	(1,500,000)	(16,300,000)
Agency RMBS
Securities, Available-for-sale [Line Items]
Proceeds	128,510,000	10,675,000	620,728,000	1,438,469,000
Available-for-sale Securities, Gross Realized Gains	831,000	2,467,000	4,171,000	15,982,000
Available-for-sale Securities, Gross Realized Losses	(1,860,000)	(564,000)	(9,114,000)	(3,369,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	(1,029,000)	1,903,000	(4,943,000)	12,613,000
Non-Agency RMBS and CMBS
Securities, Available-for-sale [Line Items]
Proceeds	55,122,000	17,926,000	196,874,000	116,349,000
Available-for-sale Securities, Gross Realized Gains	3,887,000	1,669,000	13,396,000	11,081,000
Available-for-sale Securities, Gross Realized Losses	(1,081,000)	(171,000)	(2,598,000)	(3,880,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	2,806,000	1,498,000	10,798,000	7,201,000
CLOs
Securities, Available-for-sale [Line Items]
Proceeds	0	0	129,001,000	41,714,000
Available-for-sale Securities, Gross Realized Gains	2,846,000	0	3,882,000	1,122,000
Available-for-sale Securities, Gross Realized Losses	0	256,000	(973,000)	(2,928,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	2,846,000	256,000	2,909,000	(1,806,000)
Other Securities
Securities, Available-for-sale [Line Items]
Proceeds	145,131,000	11,861,000	169,812,000	169,172,000
Available-for-sale Securities, Gross Realized Gains	2,460,000	373,000	2,705,000	1,273,000
Available-for-sale Securities, Gross Realized Losses	(313,000)	(74,000)	(185,000)	(329,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	$ 2,147,000	$ 299,000	$ 2,520,000	$ 944,000