Allowance for Loan Losses - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018 USD ($) Category	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Number of categories occupied under commercial real estate loans | Category	2
Originated [Member]
Loans and Leases Receivable Disclosure [Line Items]
Impaired TDR Loans	$ 9,450,000	$ 12,517,000	$ 12,802,000
Obligations to lend additional funds on TDR	0	1,000	0
PNCI [Member]
Loans and Leases Receivable Disclosure [Line Items]
Impaired TDR Loans	1,459,000	1,352,000	1,627,000
Obligations to lend additional funds on TDR	$ 0	$ 0	$ 2,000
Minimum [Member]
Loans and Leases Receivable Disclosure [Line Items]
Period of collateral payment of loan	3 months
Maximum [Member]
Loans and Leases Receivable Disclosure [Line Items]
Period of collateral payment of loan	12 months