Derivative Financial Instruments - Information about Interest Rate Swap Agreements (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024
Derivative [Line Items]
Notional Amount	$ 32,819,000	$ 36,184,000
Average Maturity (in years)	2 years 2 months 12 days	2 years 2 months 12 days
Estimated fair value gain (loss)	$ 12,000	$ (1,000)
Fair value hedges:
Derivative [Line Items]
Impact of estimated fair value gain (losses) on hedging instruments	71,000	(153,000)
Cash flow hedges:
Derivative [Line Items]
Impact of estimated fair value gain (losses) on hedging instruments	(6,000)	(136,000)
Interest Payments On Variable Rate Commercial Real Estate Loans | Cash flow hedges:
Derivative [Line Items]
Notional Amount	$ 27,469,000	$ 30,819,000
Average Maturity (in years)	1 year 6 months	1 year 7 months 6 days
Fixed	3.54%	3.41%
Variable	4.33%	4.47%
Estimated fair value gain (loss)	$ 3,000	$ 1,000
Fixed Rate Long-Term Borrowings | Fair value hedges:
Derivative [Line Items]
Notional Amount	$ 5,350,000	$ 5,350,000
Average Maturity (in years)	5 years 7 months 6 days	5 years 10 months 24 days
Fixed	3.55%	3.55%
Variable	4.43%	4.71%
Estimated fair value gain (loss)	$ 9,000	$ (2,000)
Fixed Rate Available For Sale Securities | Fair value hedges:
Derivative [Line Items]
Notional Amount		$ 15,000
Average Maturity (in years)		1 month 6 days
Fixed		4.84%
Variable		4.36%
Estimated fair value gain (loss)		$ 0