Disclosures About Fair Value of Financial Instruments - Summary of Financial Assets and Financial Liabilities Measured at Fair Value on Recurring and Nonrecurring Basis (Detail) $ in Thousands	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 2,746,728	$ 2,961,015
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	42,365	73,266
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	104,716	160,542
Asset-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 42,365	$ 73,266
Minimum | Asset-backed securities | Significant Unobservable Inputs (Level 3) | Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.10	0.09
Minimum | Asset-backed securities | Significant Unobservable Inputs (Level 3) | Annualized loss rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.03	0.04
Minimum | Asset-backed securities | Significant Unobservable Inputs (Level 3) | Constant prepayment rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.12	0.19
Maximum | Asset-backed securities | Significant Unobservable Inputs (Level 3) | Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.10	0.09
Maximum | Asset-backed securities | Significant Unobservable Inputs (Level 3) | Annualized loss rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.06	0.05
Maximum | Asset-backed securities | Significant Unobservable Inputs (Level 3) | Constant prepayment rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.30	0.25
Weighted Average | Asset-backed securities | Significant Unobservable Inputs (Level 3) | Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.10	0.09
Weighted Average | Asset-backed securities | Significant Unobservable Inputs (Level 3) | Annualized loss rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.05	0.05
Weighted Average | Asset-backed securities | Significant Unobservable Inputs (Level 3) | Constant prepayment rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities, available-for-sale, measurement input	0.25	0.23