Loans and Allowance for Credit Losses - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Proceeds from sales of loans held for sale			$ 299,132,000	$ 55,714,000
Non- Accrual Loans	$ 82,245,000		82,245,000		$ 56,347,000
Restructured loans	11,800,000		11,800,000		19,800,000
Total Past Due	108,280,000		108,280,000		79,910,000
Non accrual loans with no related allowance for credit losses	56,227,000		56,227,000
Accrued interest on loans	52,200,000		$ 52,200,000
Number of reasonable and supportable forecast period			1 year
Outstanding commitments to lend to borrowers with loan modifications classified as TDR's	$ 0	$ 0	$ 0	$ 0
Number of Contracts	1	0	1	0
Default payment of troubled restructuring, residential real estate loan	$ 441,000	$ 0	$ 441,000	$ 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
Impaired Loans With Associated Allowance [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans associated allowance			$ 300,000
Greater than 90 days Past Due and Accruing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Past Due	$ 4,588,000		4,588,000		$ 2,069,000
Consumer Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Proceeds from sales of loans held for sale			$ 299,100,000	$ 55,700,000