Mortgage-Backed Securities - Investment Type (Details) - USD ($) $ in Thousands		Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		$ 6,046,940	$ 6,143,945
Amortized Cost		6,172,124	6,283,185
Fair Value		5,840,559	6,038,948
Amortized cost		1,099,142	1,131,769
Gross Unrealized Gain		1,505	1,324
Gross Unrealized Loss		(177,275)	(159,826)
Fair Value		923,372	973,267
Amortized Cost		5,072,982	5,151,416
Gross Unrealized Gain		22,675	48,461
Gross Unrealized Loss		(178,470)	(134,196)
Fair Value		4,917,187	5,065,681
Residential Mortgage Backed Securities [Member] | Agency MBS
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		5,928,956	6,022,502
Amortized Cost		5,900,650	5,993,922
Fair Value		5,583,208	5,763,532
Amortized cost		882,334	898,420
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(165,983)	(148,606)
Fair Value		716,351	749,814
Amortized Cost		5,018,316	5,095,502
Gross Unrealized Gain		22,675	48,459
Gross Unrealized Loss		(174,134)	(130,243)
Fair Value		4,866,857	5,013,718
Commercial Mortgage Backed Securities [Member] | Agency MBS
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		117,984	121,293
Amortized Cost		118,473	121,799
Fair Value		111,762	115,595
Amortized cost		103,209	106,527
Gross Unrealized Gain		0	28
Gross Unrealized Loss		(5,448)	(5,159)
Fair Value		97,761	101,396
Amortized Cost		15,264	15,272
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(1,263)	(1,073)
Fair Value		14,001	14,199
Interest-Only-Strip [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Amortized Cost	[1]	153,001	167,314
Fair Value	[1]	145,589	159,718
Amortized cost		113,599	126,672
Gross Unrealized Gain		1,505	1,296
Gross Unrealized Loss		(5,844)	(6,014)
Fair Value		109,260	121,954
Amortized Cost		39,402	40,642
Gross Unrealized Gain		0	2
Gross Unrealized Loss		(3,073)	(2,880)
Fair Value		36,329	37,764
Interest-Only-Strip, Agency CMBS [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Notional balance		7,594,510	7,723,379
Interest-Only-Strip, Non-Agency CMBS [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Notional balance		3,529,181	3,860,007
Non-Agency MBS
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		0	150
Fair Value		0	103
Amortized cost		0	150
Gross Unrealized Gain		0	0
Gross Unrealized Loss		0	(47)
Fair Value		$ 0	$ 103

[1] (1) The notional balance for Agency CMBS IO and non-Agency CMBS IO was $7,594,510 and $3,529,181, respectively, as of March 31, 2024, and $7,723,379 and $3,860,007, respectively, as of December 31, 2023.