Fair Value - Summary of Changes in Fair Value Included in Current Period Results of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Credit Risk Transfer Strips [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	$ 14,489	$ 21,218	$ 67,585	$ 104,130
Credit Risk Transfer Strips [Member] | Net Gains (Losses) on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	14,489	21,218	67,585	104,130
Credit Risk Transfer Strips [Member] | Net Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Credit Risk Transfer Strips [Member] | Net Loan Servicing Fees [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Credit Risk Transfer Strips [Member] | Net Interest Income (Expense) [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Interest-only security payable [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(2,390)	(4,228)	(2,431)	(6,363)
Interest-only security payable [Member] | Net Gains (Losses) on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(2,390)	(4,228)	(2,431)	(6,363)
Interest-only security payable [Member] | Net Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Interest-only security payable [Member] | Net Loan Servicing Fees [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Interest-only security payable [Member] | Net Interest Income (Expense) [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Asset-Backed Financings of VIEs at Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(71,896)	59,606	(63,013)	66,774
Asset-Backed Financings of VIEs at Fair Value [Member] | Net Gains (Losses) on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(72,922)	58,474	(64,151)	66,108
Asset-Backed Financings of VIEs at Fair Value [Member] | Net Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Asset-Backed Financings of VIEs at Fair Value [Member] | Net Loan Servicing Fees [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Asset-Backed Financings of VIEs at Fair Value [Member] | Net Interest Income (Expense) [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	1,026	1,132	1,138	666
Liabilities, Total [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(74,286)	55,378	(65,444)	60,411
Liabilities, Total [Member] | Net Gains (Losses) on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(75,312)	54,246	(66,582)	59,745
Liabilities, Total [Member] | Net Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Liabilities, Total [Member] | Net Loan Servicing Fees [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Liabilities, Total [Member] | Net Interest Income (Expense) [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	1,026	1,132	1,138	666
Mortgage-backed securities at fair value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	139,096	(142,983)	75,650	(128,606)
Mortgage-backed securities at fair value [Member] | Net Gains (Losses) on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	123,433	(144,031)	50,310	(127,434)
Mortgage-backed securities at fair value [Member] | Net Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Mortgage-backed securities at fair value [Member] | Net Loan Servicing Fees [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Mortgage-backed securities at fair value [Member] | Net Interest Income (Expense) [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	15,663	1,048	25,340	(1,172)
Loans acquired for sale at fair value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	65,611	(13,106)	67,243	(7,215)
Loans acquired for sale at fair value [Member] | Net Gains (Losses) on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Loans acquired for sale at fair value [Member] | Net Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	65,611	(13,106)	67,243	(7,215)
Loans acquired for sale at fair value [Member] | Net Loan Servicing Fees [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Loans acquired for sale at fair value [Member] | Net Interest Income (Expense) [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
At fair value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	77,579	(59,294)	70,819	(68,015)
At fair value [Member] | Net Gains (Losses) on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	75,350	(54,141)	71,330	(61,803)
At fair value [Member] | Net Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
At fair value [Member] | Net Loan Servicing Fees [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
At fair value [Member] | Net Interest Income (Expense) [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	2,229	(5,153)	(511)	(6,212)
MSRs at fair value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(184,918)	160,926	(263,676)	(64,515)
MSRs at fair value [Member] | Net Gains (Losses) on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
MSRs at fair value [Member] | Net Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
MSRs at fair value [Member] | Net Loan Servicing Fees [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(184,918)	160,926	(263,676)	(64,515)
MSRs at fair value [Member] | Net Interest Income (Expense) [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	0	0	0	0
Assets, Total [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	111,857	(33,239)	17,621	(164,221)
Assets, Total [Member] | Net Gains (Losses) on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	213,272	(176,954)	189,225	(85,107)
Assets, Total [Member] | Net Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	65,611	(13,106)	67,243	(7,215)
Assets, Total [Member] | Net Loan Servicing Fees [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(184,918)	160,926	(263,676)	(64,515)
Assets, Total [Member] | Net Interest Income (Expense) [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	$ 17,892	$ (4,105)	$ 24,829	$ (7,384)