Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Derivative [Line Items]
Notional Amount	$ 30,570,000	$ 26,977,000
Average Maturity (in years)	2 years	2 years 2 months 12 days
Estimated fair value gain (loss)	$ (38,000)	$ 10,000
Interest Payments On Variable Rate Commercial Real Estate Loans | Cash flow hedges:
Derivative [Line Items]
Notional Amount	$ 26,705,000	$ 23,977,000
Average Maturity (in years)	1 year 6 months	1 year 8 months 12 days
Fixed	3.39%	3.45%
Variable	5.02%	5.36%
Estimated fair value gain (loss)	$ (30,000)	$ 11,000
Fixed Rate Long-Term Borrowings | Fair value hedges:
Derivative [Line Items]
Notional Amount	$ 3,850,000	$ 3,000,000
Average Maturity (in years)	5 years 4 months 24 days	5 years 9 months 18 days
Fixed	3.48%	3.45%
Variable	5.06%	5.62%
Estimated fair value gain (loss)	$ (8,000)	$ (1,000)
Fixed Rate Available For Sale Securities | Fair value hedges:
Derivative [Line Items]
Notional Amount	$ 15,000
Average Maturity (in years)	3 months 18 days
Fixed	4.84%
Variable	4.86%
Estimated fair value gain (loss)	$ 0