Loans and Allowance for Credit Losses - Additional Information (Detail)	3 Months Ended	12 Months Ended
Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Proceeds from sales of loans held for sale	$ 43,163,000	$ 75,667,000
Nonaccrual Loans	76,706,000		$ 87,823,000
Restructured loans	7,900,000		10,800,000
Total Past Due	97,339,000		99,644,000
Non accrual loans with no related allowance for credit losses	34,100,000		42,122,000
Accrued interest on loans	$ 60,800,000		58,800,000
Number of reasonable and supportable forecast period	1 year
Commitments to lend to borrowers with loan modifications classified as TDR's	$ 0	$ 0
Number of Contracts	0	0
Default payment of troubled restructuring	$ 0	$ 0
Minimum [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of reasonable and supportable forecast period	1 year
Maximum [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of reasonable and supportable forecast period	3 years
Individually Evaluated Loans and Collateral Dependent Assets [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans associated allowance	$ 600,000		600,000
Greater than 90 days Past Due and Accruing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Past Due	1,773,000		$ 1,952,000
Consumer Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Proceeds from sales of loans held for sale	$ 43,200,000	$ 75,700,000

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Amount of addition to allowance reserve for credit loss arising from purchase of loan and lease portfolios.

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Number of financing receivables that have been modified by troubled debt restructurings.

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Amount of financing receivable on nonaccrual status with no allowance for credit loss.

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Amount of financing receivable on nonaccrual status.

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Amount of financing receivable past due.

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Amount of unfunded portion of contractual agreement to lend funds to borrower for financing receivable modified as troubled debt restructuring.

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The cash inflow resulting from the sale of loans classified as held-for-sale, including proceeds from loans sold through mortgage securitization.

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