Commitments and Contingent Liabilities - Additional Information (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Notional Amount Of Performance Standby Letters Of Credit	$ 700,000
Notional Amount Of Commercial Letters Of Credit	0
Notional Amount Of Financial Standby Letters Of Credit	1,100,000
Financial instrument of credit risk	200,000	$ 200,000
Unfunded commitment liability	5,200,000	$ 5,200,000
Minimum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	0
Maximum [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	$ 1,000,000