Loans and Allowance for Credit Losses - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Proceeds from sales of loans held for sale	$ 133,182,000	$ 213,093,000	$ 59,138,000
Nonaccrual Loans	87,823,000	56,347,000
Restructured loans	10,800,000	19,800,000
Total Past Due	99,644,000	79,910,000
Accrued interest on loans	$ 58,800,000
Number of reasonable and supportable forecast period	1 year
Outstanding commitments to lend to borrowers with loan modifications classified as TDR's	$ 0	0
Number of contracts added	1
Default payment of troubled restructuring	$ 0	$ 0
Real Estate Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Default payment of troubled restructuring	$ 441,000
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts added		2
Default payment of troubled restructuring		$ 11,500,000
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of contracts added		1
Default payment of troubled restructuring		$ 3,100,000
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
Impaired Loans With Associated Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans associated allowance	$ 600,000
Greater than 90 days Past Due and Accruing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Past Due	$ 1,952,000	$ 2,069,000