Investment Securities - Additional Information (Detail)		3 Months Ended			9 Months Ended
	Jun. 30, 2023 USD ($)	Sep. 30, 2023 USD ($) security corporateNote assetBackedSecurity	Jun. 30, 2023 USD ($)	Sep. 30, 2022 USD ($) assetBackedSecurity	Sep. 30, 2023 USD ($) security corporateNote assetBackedSecurity	Sep. 30, 2022 USD ($) assetBackedSecurity	Dec. 31, 2022 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Proceeds from sales of investment securities available for sale		$ 4,100,000		$ 126,600,000	$ 4,075,000	$ 681,633,000
Number of available-for-sale investment securities, unrealized loss position, less than twelve month category | security		25			25
Number of available-for-sale investment securities, unrealized loss position, twelve month or more category | security		155			155
Number of asset-backed securities with deterioration in future estimated cash flows | assetBackedSecurity		4		4	4	4
Number of corporate notes with deterioration in future estimated cash flows | corporateNote		12			12
Number of available-for-sale investment securities, unrealized loss position | security		180			180		156
Debt securities, available for sale		$ 2,746,728,000			$ 2,746,728,000		$ 2,961,015,000
Debt securities, held-to-maturity, allowance for credit loss, excluding accrued interest		0			0		0
Carrying value of consumer loans sold				$ 521,800,000		$ 521,800,000
Net loss on sale of loans					1,200,000
Investment securities held to maturity		1,178,370,000			1,178,370,000		840,259,000
Servicing assets		3,800,000			3,800,000
Variable Interest Entity, Not Primary Beneficiary
Debt Securities, Available-for-sale [Line Items]
Investment securities held to maturity		436,800,000			436,800,000
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, available for sale		104,716,000			104,716,000		160,542,000
Debt securities, held-to-maturity, allowance for credit loss, excluding accrued interest		0			0		0
Investment securities held to maturity		645,362,000			645,362,000		361,107,000
Consumer Loan, Held-For-Sale | Personal And Other Installment Loans
Debt Securities, Available-for-sale [Line Items]
Carrying value of consumer loans sold	$ 556,700,000
Consumer Loan, Held-For-Sale | Other Installment Loans
Debt Securities, Available-for-sale [Line Items]
Carrying value of consumer loans sold			$ 154,000,000
Asset Pledged as Collateral
Debt Securities, Available-for-sale [Line Items]
Debt securities, available for sale		1,500,000,000			1,500,000,000
Debt securities		$ 402,600,000			$ 402,600,000		$ 16,700,000