Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018 USD ($) Category	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Number of categories occupied under commercial real estate loans | Category	2
Originated Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Impaired TDR Loans	$ 9,781,000	$ 12,517,000	$ 12,285,000
Additional funds in TDR	1,000	1,000	70,000
PNCI Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Impaired TDR Loans	1,471,000	1,352,000	1,470,000
Obligations to lend additional funds on TDR	$ 0	$ 0	$ 0
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