Fair Value - Summary of Changes in Items Measured Using Level 3 Inputs on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Assets:
Amounts received pursuant to sales of loans	$ 87,588	$ 58,560	$ 159,456	$ 249,925
Changes in fair value included in income arising from:
Loans to REO			0	(1,182)
Mortgage servicing rights relating to delinquent loans to Agency			$ 341	$ (653)
Liabilities:
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Gain (Loss) on Investments	Gain (Loss) on Investments	Gain (Loss) on Investments	Gain (Loss) on Investments
Interest Rate Lock Commitments [Member]
Assets:
Beginning balance			$ 7,532
Changes in fair value included in income arising from:
Ending balance	$ 5,902		5,902
Recurring [Member]
Assets:
Beginning balance	4,048,577	$ 3,902,972	3,998,787	$ 3,867,133
Purchases and issuances (purchase adjustments)	18,815	22,881	61,611	23,331
Repayments and sales	(56,593)	(17,162)	(100,876)	(58,133)
Accrual of unearned discounts	2,264		6,870
Amounts received pursuant to sales of loans	87,588	58,064	159,456	249,429
Changes in fair value included in income arising from:
Changes in instrument-specific credit risk	0	0	0	0
Other factors	(137,940)	179,112	(154,504)	74,856
Total	(137,940)	179,112	(154,504)	74,856
Exchange of mortgage servicing spread for interest-only stripped mortgage-backed securities	0	(1,549)	0	(1,549)
Loans to REO				(460)
Interest rate lock commitments to loans acquired for sale	(42,397)	7,587	(51,246)	(1,979)
Mortgage servicing rights relating to delinquent loans to Agency	125	70	341	(653)
Ending balance	3,920,439	4,151,975	3,920,439	4,151,975
Changes in fair value recognized during the quarter relating to assets	(170,023)	176,476	(213,607)	26,258
Recurring [Member] | CRT Derivatives [Member]
Assets:
Beginning balance	24,305	(4,394)	16,160	(22,098)
Purchases and issuances (purchase adjustments)	0	0	0	0
Repayments and sales	(3,350)	(4,028)	(10,434)	(12,283)
Accrual of unearned discounts	0		0
Amounts received pursuant to sales of loans	0	0	0	0
Changes in fair value included in income arising from:
Changes in instrument-specific credit risk	0	0	0	0
Other factors	8,735	13,164	23,964	39,123
Total	8,735	13,164	23,964	39,123
Exchange of mortgage servicing spread for interest-only stripped mortgage-backed securities	0	0	0	0
Loans to REO				0
Interest rate lock commitments to loans acquired for sale	0	0	0	0
Mortgage servicing rights relating to delinquent loans to Agency	0	0	0	0
Ending balance	29,690	4,742	29,690	4,742
Changes in fair value recognized during the quarter relating to assets	5,460	9,113	13,716	26,619
Recurring [Member] | Credit Risk Transfer Strips [Member]
Assets:
Beginning balance	(16,974)	(78,569)	(46,692)	(137,193)
Purchases and issuances (purchase adjustments)	0	0	0	0
Repayments and sales	(10,990)	(11,241)	(34,368)	(35,529)
Accrual of unearned discounts	0		0
Amounts received pursuant to sales of loans	0	0	0	0
Changes in fair value included in income arising from:
Changes in instrument-specific credit risk	0	0	0	0
Other factors	14,489	21,218	67,585	104,130
Total	14,489	21,218	67,585	104,130
Exchange of mortgage servicing spread for interest-only stripped mortgage-backed securities	0	0	0	0
Loans to REO				0
Interest rate lock commitments to loans acquired for sale	0	0	0	0
Mortgage servicing rights relating to delinquent loans to Agency	0	0	0	0
Ending balance	(13,475)	(68,592)	(13,475)	(68,592)
Changes in fair value recognized during the quarter relating to assets	3,499	9,977	33,217	68,601
Recurring [Member] | Loans At Fair Value [Member]
Assets:
Beginning balance	1,998	2,665	2,131	3,457
Purchases and issuances (purchase adjustments)	0	0	0	119
Repayments and sales	(38)	(510)	(129)	(534)
Accrual of unearned discounts	0		0
Amounts received pursuant to sales of loans	0	0	0	0
Changes in fair value included in income arising from:
Changes in instrument-specific credit risk	0	0	0	0
Other factors	(10)	(58)	(52)	(485)
Total	(10)	(58)	(52)	(485)
Exchange of mortgage servicing spread for interest-only stripped mortgage-backed securities	0	0	0	0
Loans to REO				(460)
Interest rate lock commitments to loans acquired for sale	0	0	0	0
Mortgage servicing rights relating to delinquent loans to Agency	0	0	0	0
Ending balance	1,950	2,097	1,950	2,097
Changes in fair value recognized during the quarter relating to assets	(19)	(74)	(71)	(1,011)
Recurring [Member] | Mortgage servicing rights [Member]
Assets:
Beginning balance	3,941,861	3,977,938	3,919,107	4,012,737
Purchases and issuances (purchase adjustments)	0	16,263	29,428	16,263
Repayments and sales	0	0	0	0
Accrual of unearned discounts	0		0
Amounts received pursuant to sales of loans	87,588	58,560	159,456	249,925
Changes in fair value included in income arising from:
Changes in instrument-specific credit risk	0	0	0	0
Other factors	(184,918)	160,926	(263,676)	(64,515)
Total	(184,918)	160,926	(263,676)	(64,515)
Exchange of mortgage servicing spread for interest-only stripped mortgage-backed securities	(35,609)	(105,096)	(35,609)	(105,096)
Loans to REO				0
Interest rate lock commitments to loans acquired for sale	0	0	0	0
Mortgage servicing rights relating to delinquent loans to Agency	125	70	341	(653)
Ending balance	3,809,047	4,108,661	3,809,047	4,108,661
Changes in fair value recognized during the quarter relating to assets	(180,885)	160,926	(261,304)	(64,515)
Recurring [Member] | Interest-Only Stripped Mortgage-Backed Securities [Member]
Assets:
Beginning balance	87,841	0	94,231	0
Purchases and issuances (purchase adjustments)	0	0	0	0
Repayments and sales	(40,487)	0	(50,541)	0
Accrual of unearned discounts	2,264		6,870
Amounts received pursuant to sales of loans	0	0	0	0
Changes in fair value included in income arising from:
Changes in instrument-specific credit risk	0	0	0	0
Other factors	(3,971)	(14)	(4,913)	(14)
Total	(3,971)	(14)	(4,913)	(14)
Exchange of mortgage servicing spread for interest-only stripped mortgage-backed securities	35,609	103,547	35,609	103,547
Loans to REO				0
Interest rate lock commitments to loans acquired for sale	0	0	0	0
Mortgage servicing rights relating to delinquent loans to Agency	0	0	0
Ending balance	81,256	103,533	81,256	103,533
Changes in fair value recognized during the quarter relating to assets	(3,971)	(14)	(4,913)	(14)
Recurring [Member] | Loans acquired for sale [Member]
Assets:
Beginning balance	7,994	6,630	6,318	10,708
Purchases and issuances (purchase adjustments)	(156)	0	5,341	4,262
Repayments and sales	(1,728)	(1,383)	(5,404)	(9,787)
Accrual of unearned discounts	0		0
Amounts received pursuant to sales of loans	0	(496)	0	(496)
Changes in fair value included in income arising from:
Changes in instrument-specific credit risk	0	0	0	0
Other factors	(41)	131	(186)	195
Total	(41)	131	(186)	195
Exchange of mortgage servicing spread for interest-only stripped mortgage-backed securities	0	0	0	0
Loans to REO				0
Interest rate lock commitments to loans acquired for sale	0	0	0	0
Mortgage servicing rights relating to delinquent loans to Agency	0	0	0
Ending balance	6,069	4,882	6,069	4,882
Changes in fair value recognized during the quarter relating to assets	(9)	(104)	(154)	(74)
Recurring [Member] | Interest Rate Lock Commitments [Member]
Assets:
Beginning balance	1,552	(1,298)	7,532	(478)
Purchases and issuances (purchase adjustments)	18,971	6,618	26,842	2,687
Repayments and sales	0	0	0	0
Accrual of unearned discounts	0		0
Amounts received pursuant to sales of loans	0	0	0	0
Changes in fair value included in income arising from:
Changes in instrument-specific credit risk	0	0	0	0
Other factors	27,776	(16,255)	22,774	(3,578)
Total	27,776	(16,255)	22,774	(3,578)
Exchange of mortgage servicing spread for interest-only stripped mortgage-backed securities	0	0	0	0
Loans to REO				0
Interest rate lock commitments to loans acquired for sale	(42,397)	7,587	(51,246)	(1,979)
Mortgage servicing rights relating to delinquent loans to Agency	0	0	0	0
Ending balance	5,902	(3,348)	5,902	(3,348)
Changes in fair value recognized during the quarter relating to assets	5,902	(3,348)	5,902	(3,348)
Recurring [Member] | Interest-only security payable [Member]
Liabilities:
Beginning balance	32,708	24,060	32,667	21,925
Changes in instrument-specific credit risk\Other factors	2,390	4,228	2,431	6,363
Ending balance	35,098	28,288	35,098	28,288
Changes in fair value recognized during the quarter relating to liability	2,390	4,228	2,431	6,363
Recurring [Member] | Interest-only security payable [Member] | Credit Risk [Member]
Liabilities:
Changes in instrument-specific credit risk\Other factors	0	0	0	0
Recurring [Member] | Interest-only security payable [Member] | Other Factors [Member]
Liabilities:
Changes in instrument-specific credit risk\Other factors	$ 2,390	$ 4,228	$ 2,431	$ 6,363