Allowance for Loan Losses - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2017 USD ($) Category	Dec. 31, 2016 USD ($)	Sep. 30, 2016 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	$ 13,352,000	$ 12,371,000	$ 14,882,000
Additional funds in TDR	3,000	25,000	65,000
PNCI Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Impaired TDR Loans	1,611,000	1,324,000	1,476,000
Obligations to lend additional funds on TDR	$ 209,000	$ 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