Commitments and Contingencies (Summary of Bank's Commitments) (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off balance sheet risk	$ 55,081	$ 58,018
Standby Letters of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off balance sheet risk	1,247	1,106
Commitments to Extend Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off balance sheet risk	$ 53,834	$ 56,912