Fair Value - Key Assumptions Used in Determining Fair Value of MSRs at Time of Initial Recognition (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024 USD ($) UsdPerLoan	Sep. 30, 2023 USD ($) UsdPerLoan	Sep. 30, 2024 USD ($) UsdPerLoan	Sep. 30, 2023 USD ($) UsdPerLoan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, MSR recognized | $	$ 87,588	$ 58,560	$ 159,456	$ 249,925
Fair value, Unpaid principal balance of underlying loans | $	$ 5,130,285	$ 3,052,557	$ 9,203,814	$ 13,458,182
Fair value, Weighted-average annual servicing fee rate (in basis points)	0.35%	0.38%	0.35%	0.40%
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value inputs, Pricing spread during period	11.70%	10.10%	10.80%	10.10%
Fair Value inputs, Prepayment speed during period	5.40%	5.50%	5.40%	5.50%
Fair Value inputs, Weighted average equivalent average life during period	3 years 6 months	3 years 2 months 12 days	3 years 4 months 24 days	2 years 9 months 18 days
Fair Value inputs, Annual per loan cost of servicing during period	68	69	68	68
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value inputs, Pricing spread during period	26.70%	22.70%	26.70%	22.70%
Fair Value inputs, Prepayment speed during period	7.30%	8.50%	8.50%	8.80%
Fair Value inputs, Weighted average equivalent average life during period	6 years 4 months 24 days	7 years 2 months 12 days	7 years 2 months 12 days	7 years 2 months 12 days
Fair Value inputs, Annual per loan cost of servicing during period	87	71	87	71
Weighted Average [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value inputs, Pricing spread during period	5.50%	5.50%	5.60%	5.80%
Fair Value inputs, Prepayment speed during period	13.60%	11.30%	13.10%	12.30%
Fair Value inputs, Weighted average equivalent average life during period	6 years 3 months 18 days	7 years 1 month 6 days	6 years 6 months	6 years 9 months 18 days
Fair Value inputs, Annual per loan cost of servicing during period	68	71	69	69