Commitments and Contingent Liabilities - Additional Information (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Notional Amount Of Performance Standby Letters Of Credit	$ 1,300,000
Notional Amount Of Commercial Letters Of Credit	0
Notional Amount Of Financial Standby Letters Of Credit	1,300,000
Financial instrument of credit risk	200,000	$ 200,000
Unfunded commitment liability	4,600,000	$ 4,100,000
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	$ 7,000,000