Fair Value - Summary of Changes in Fair Value Included in Current Period Results of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Credit Risk Transfer Strips [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	$ 12,071	$ 46,480	$ 53,096	$ 82,912
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 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 (Losses) Gains on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	12,071	46,480	53,096	82,912
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)	(481)	(855)	(41)	(2,135)
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 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 (Losses) Gains on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(481)	(855)	(41)	(2,135)
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)	691	17,870	8,659	7,168
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 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 (Losses) Gains on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	1,295	17,794	8,771	7,634
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)	(604)	76	(112)	(466)
Liabilities, Total [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	210	17,015	8,618	5,033
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 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
Liabilities, Total [Member] | Net (Losses) Gains on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	814	16,939	8,730	5,499
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)	(604)	76	(112)	(466)
Mortgage-backed securities at fair value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(28,339)	(61,885)	(63,446)	14,377
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 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 (Losses) Gains on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(34,925)	(61,621)	(73,123)	16,597
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)	6,586	(264)	9,677	(2,220)
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)	1,969	(9,424)	1,632	5,891
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 Gains on Loans Acquired for Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	1,969	(9,424)	1,632	5,891
Loans acquired for sale at fair value [Member] | Net (Losses) Gains 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 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)	(3,347)	(20,315)	(6,760)	(8,721)
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 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 (Losses) Gains on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(2,742)	(19,130)	(4,020)	(7,662)
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)	(605)	(1,185)	(2,740)	(1,059)
MSRs at fair value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(50,556)	(87,997)	(78,758)	(225,441)
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)	(50,556)	(87,997)	(78,758)	(225,441)
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 (Losses) Gains 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 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)	(68,202)	(133,141)	(94,236)	(130,982)
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)	(50,556)	(87,997)	(78,758)	(225,441)
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)	1,969	(9,424)	1,632	5,891
Assets, Total [Member] | Net (Losses) Gains on Investments and Financings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Changes in fair value included in current period income (expense)	(25,596)	(34,271)	(24,047)	91,847
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)	$ 5,981	$ (1,449)	$ 6,937	$ (3,279)