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Loans and allowance for loan losses - Effect of Loan Modification on Weighted-average Remaining Life (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Weighted-average remaining term	3 months 18 days	1 year 3 months 18 days	8 months 12 days	1 year
Commercial Real Estate
Financing Receivable, Modifications [Line Items]
Weighted-average remaining term	8 months 12 days	7 months 6 days	9 months 18 days	9 months 18 days
Residential Real Estate
Financing Receivable, Modifications [Line Items]
Weighted-average remaining term	9 years 10 months 24 days	9 years 1 month 6 days	10 years 1 month 6 days	9 years 10 months 24 days

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