Mortgage-Backed Securities - Investment Type (Details) - USD ($) $ in Thousands		Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		$ 7,355,891	$ 6,143,945
Amortized Cost		7,468,566	6,283,185
Non-Agency other, Amortized Cost		1,036,447	1,131,769
Fair Value		7,327,643	6,038,948
Gross Unrealized Gain		1,913	1,324
Gross Unrealized Loss		(137,802)	(159,826)
Fair Value		900,558	973,267
Amortized Cost		6,432,119	5,151,416
Gross Unrealized Gain		98,269	48,461
Gross Unrealized Loss		(103,303)	(134,196)
Fair Value		6,427,085	5,065,681
Residential Mortgage Backed Securities [Member] | Agency MBS
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		7,254,934	6,022,502
Amortized Cost		7,239,866	5,993,922
Non-Agency other, Amortized Cost		844,694	898,420
Fair Value		7,105,090	5,763,532
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(131,398)	(148,606)
Fair Value		713,296	749,814
Amortized Cost		6,395,172	5,095,502
Gross Unrealized Gain		98,267	48,459
Gross Unrealized Loss		(101,645)	(130,243)
Fair Value		6,391,794	5,013,718
Commercial Mortgage Backed Securities [Member] | Agency MBS
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		100,957	121,293
Amortized Cost		101,169	121,799
Non-Agency other, Amortized Cost		101,169	106,527
Fair Value		98,026	115,595
Gross Unrealized Gain		8	28
Gross Unrealized Loss		(3,151)	(5,159)
Fair Value		98,026	101,396
Amortized Cost			15,272
Gross Unrealized Gain			0
Gross Unrealized Loss			(1,073)
Fair Value			14,199
Interest-Only-Strip [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Amortized Cost	[1]	127,531	167,314
Non-Agency other, Amortized Cost		90,584	126,672
Fair Value	[1]	124,527	159,718
Gross Unrealized Gain		1,905	1,296
Gross Unrealized Loss		(3,253)	(6,014)
Fair Value		89,236	121,954
Amortized Cost		36,947	40,642
Gross Unrealized Gain		2	2
Gross Unrealized Loss		(1,658)	(2,880)
Fair Value		35,291	37,764
Interest-Only-Strip, Agency CMBS [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		6,802,508	7,723,379
Interest-Only-Strip, Non-Agency CMBS [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		2,784,032	3,860,007
Non-Agency MBS
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		0	150
Non-Agency other, Amortized Cost		0	150
Gross Unrealized Gain			0
Gross Unrealized Loss			(47)
Fair Value		$ 0	$ 103

[1] (1) The notional balance for Agency CMBS IO and non-Agency CMBS IO was $6,802,508 and $2,784,032, respectively, as of September 30, 2024, and $7,723,379 and $3,860,007, respectively, as of December 31, 2023.