Derivative and Credit Risk Transfer Strip Assets and Liabilities - Derivative Assets and Derivative Liabilities and Related Margin Deposits (Detail) - USD ($)		Sep. 30, 2024	Dec. 31, 2023
Derivatives Fair Value [Line Items]
Total derivatives assets before netting		$ 66,103,000	$ 89,591,000
Derivative assets, Netting		15,741,000	88,393,000
Total derivative assets after netting		81,844,000	177,984,000
Margin deposits placed with derivative counterparties included in derivative balances above, net		33,620,000	137,955,000
Derivative assets pledged to secure:
Notes payable secured by credit risk transfer and mortgage servicing assets		2,830,108,000	2,910,605,000
Total derivative liabilities		20,556,000	54,250,000
Derivative liabilities, Netting		(17,880,000)	(49,561,000)
Total derivative liabilities after netting		2,676,000	4,689,000
Derivative assets related to CRT Derivatives [Member]
Derivative assets pledged to secure:
Notes payable secured by credit risk transfer and mortgage servicing assets		29,690,000	16,160,000
CRT Derivatives [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1]	5,071,449,000	5,437,551,000
Total derivatives assets before netting	[2]	29,690,000	16,160,000
Total derivative assets after netting		29,690,000	16,160,000
Derivative assets pledged to secure:
Total derivative liabilities	[2]	0	0
Forward Purchase Contracts [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1],[2]	3,194,957,000	2,789,324,000
Total derivatives assets before netting	[2]	635,000	15,905,000
Derivative assets pledged to secure:
Total derivative liabilities	[2]	7,452,000	490,000
Forward Sale Contracts [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1],[2]	9,672,080,000	7,219,512,000
Total derivatives assets before netting	[2]	11,997,000	671,000
Derivative assets pledged to secure:
Total derivative liabilities	[2]	11,530,000	50,363,000
Interest Rate Lock Commitments [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1]	2,062,088,000	874,017,000
Total derivatives assets before netting	[2]	7,476,000	7,596,000
Total derivative assets after netting		7,476,000	7,596,000
Derivative assets pledged to secure:
Total derivative liabilities	[2]	1,574,000	64,000
Call Options on Interest Rate Futures Purchase Contracts [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1],[2]	4,700,000,000	2,315,000,000
Total derivatives assets before netting	[2]	12,844,000	41,712,000
Derivative assets pledged to secure:
Total derivative liabilities	[2]	0	2,005,000
Put Options On Interest Rate Futures Purchase Contracts
Derivatives Fair Value [Line Items]
Notional amount	[1],[2]	500,000,000	2,900,000,000
Total derivatives assets before netting	[2]	1,953,000	4,324,000
Derivative assets pledged to secure:
Total derivative liabilities	[2]	0	0
Call Options On Interest Rate Futures Sell Contracts [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1],[2]	0	500,000,000
Total derivatives assets before netting	[2]	0	0
Derivative assets pledged to secure:
Total derivative liabilities	[2]	0	1,328,000
MBS Call Options [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1],[2]	0	500,000,000
Total derivatives assets before netting	[2]	0	3,218,000
Derivative assets pledged to secure:
Total derivative liabilities	[2]	0	0
MBS Put Options [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1],[2]	500,000,000	450,000,000
Total derivatives assets before netting	[2]	1,508,000	5,000
Derivative assets pledged to secure:
Total derivative liabilities	[2]	0	0
Swap Futures [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1],[2]	951,200,000	1,048,800,000
Total derivatives assets before netting	[2]	0	0
Derivative assets pledged to secure:
Total derivative liabilities	[2]	0	0
Bond Futures [Member]
Derivatives Fair Value [Line Items]
Notional amount	[1],[2]	2,096,000,000	2,860,500,000
Total derivatives assets before netting	[2]	0	0
Derivative assets pledged to secure:
Total derivative liabilities	[2]	$ 0	$ 0

[1] Notional amounts provide an indication of the volume of the Company’s derivative activities.

[2] All hedging derivatives are interest rate derivatives that are used as economic hedges.