Fair Value Measurements - Narrative (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Broker dealer deposit program fair value	$ 2,500,000
Total credit-related financial instruments with off-balance sheet risk	12,572,316		$ 12,237,964
Total write-ups	1,200
Proceeds from sales of alternative investments	4,970	$ 0
Gains on sale	3,291	$ 0
Loans transferred to held-for-sale	63,200		27,300
Amortized cost of consumer loans	12,000
Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments held in Rabbi Trust	300		400
Carrying amount of alternative investments	1,700
Proceeds from sales of alternative investments	5,000
Gains on sale	3,300
Rabbi Trust
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments held in Rabbi Trust	9,400		9,200
Alternative investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments held in Rabbi Trust	31,500		30,100
Equity investment, carrying amount	0		0
Alternative investments, carrying amount	46,500		43,400
Alternative investments | Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total credit-related financial instruments with off-balance sheet risk	69,400		61,500
Alternative investments measured at fair value	$ 5,400		$ 8,300