Loans and Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Proceeds from sales of loans held for sale			$ 24,030,000	$ 35,390,000
Non- Accrual Loans	$ 56,030,000		56,030,000		$ 59,142,000
Restructured loans	21,100,000		21,100,000		41,000,000
Total Past Due	71,781,000		71,781,000		86,369,000
Commitments to lend to borrowers with loan modifications classified as TDR's	$ 0	$ 1,600	$ 0	$ 1,600
Number of Contracts		0
Real estate - residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of Contracts	1		1
Pre-Modification Outstanding Recorded Investment	$ 93,000		$ 93,000
Post-Modification Outstanding Recorded Investment	92,000		92,000
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Non- Accrual Loans	37,568,000		37,568,000		38,644,000
Total Past Due	$ 44,096,000		$ 44,096,000		50,532,000
Number of Contracts	1		1	1
Pre-Modification Outstanding Recorded Investment	$ 6,200,000		$ 6,200,000	$ 7,200,000
Post-Modification Outstanding Recorded Investment	6,100,000		$ 6,100,000	$ 7,200,000
Revolving Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days past due to consider loan as a loss and charged off			90 days
Closed-End Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days past due to consider loan as a loss and charged off			120 days
Open-End Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days past due to consider loan as a loss and charged off			180 days
Greater than 90 days Past Due and Accruing [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Past Due	2,883,000		$ 2,883,000		3,091,000
Greater than 90 days Past Due and Accruing [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Past Due	$ 819,000		$ 819,000		$ 672,000