Mortgage-Backed Securities - Summary of Investments in Mortgage Backed Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Mortgage Backed Securities [Line Items]
Fair value	$ 4,075,660	$ 4,452,859
Mortgage Backed Securities [Member]
Mortgage Backed Securities [Line Items]
Principal balance or notional amount	4,068,803	4,421,692
Purchase premiums (discounts), net	(104,080)	(121,798)
Cumulative valuation changes	42,003	80,463
Fair value	4,006,726	4,380,357
Total	4,075,660
Maturing after one year through five years	3,992
Maturing after ten years	4,071,668
Interest-Only Stripped Securities [Member]
Mortgage Backed Securities [Line Items]
Principal balance or notional amount	320,761	344,592
Fair value	68,934	72,502
Total	68,934
Maturing after one year through five years	0
Maturing after ten years	68,934
Mortgage-Backed Securities Including Interest-Only Stripped Mortgage-Backed Securities [Member]
Mortgage Backed Securities [Line Items]
Fair value	4,075,660	4,452,859
Agency Fixed Rate Pass Through [Member] \| Mortgage Backed Securities [Member]
Mortgage Backed Securities [Line Items]
Principal balance or notional amount	2,159,819	2,805,895
Purchase premiums (discounts), net	399	(2,125)
Cumulative valuation changes	18,377	46,677
Fair value	2,178,595	2,850,447
Total	2,178,595
Maturing after one year through five years	0
Maturing after ten years	2,178,595
Floating Rate Collateralized Mortgage Obligations [Member] \| Mortgage Backed Securities [Member]
Mortgage Backed Securities [Line Items]
Principal balance or notional amount	1,282,079	850,172
Purchase premiums (discounts), net	418	(1,249)
Cumulative valuation changes	8,487	7,074
Fair value	1,290,984	855,997
Total	1,290,984
Maturing after one year through five years	0
Maturing after ten years	1,290,984
Principal-only Stripped [Member] \| Mortgage Backed Securities [Member]
Mortgage Backed Securities [Line Items]
Principal balance or notional amount	490,817	610,256
Purchase premiums (discounts), net	(102,044)	(115,385)
Cumulative valuation changes	16,175	26,258
Fair value	404,948	521,129
Total	404,948
Maturing after one year through five years	0
Maturing after ten years	404,948
Senior Non-Agency [Member] \| Mortgage Backed Securities [Member]
Mortgage Backed Securities [Line Items]
Principal balance or notional amount	132,088	155,369
Purchase premiums (discounts), net	(2,853)	(3,039)
Cumulative valuation changes	(1,028)	454
Fair value	128,207	$ 152,784
Total	128,207
Maturing after one year through five years	0
Maturing after ten years	128,207
Subordinate Residential Transition [Member] \| Mortgage Backed Securities [Member]
Mortgage Backed Securities [Line Items]
Principal balance or notional amount	4,000
Purchase premiums (discounts), net	0
Cumulative valuation changes	(8)
Fair value	3,992
Total	3,992
Maturing after one year through five years	3,992
Maturing after ten years	$ 0

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