Fair Value Measurement - Schedule of Assets Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Fair Value Inputs Asset Quantitative Information [Line Items]
Other real estate owned and repossessed assets	$ 4,384	$ 5,297
Impaired loans, Appraisal adjustments	0.00%	(4.80%)
Impaired loans, Liquidation expenses	0.00%	(7.60%)
Nonrecurring Fair Value Measurements [Member]
Fair Value Inputs Asset Quantitative Information [Line Items]
Impaired loans		$ 1,717
Other real estate owned and repossessed assets	$ 4,384	5,297
Significant Unobservable Inputs (Level 3) [Member] | Nonrecurring Fair Value Measurements [Member]
Fair Value Inputs Asset Quantitative Information [Line Items]
Impaired loans	0	1,717
Other real estate owned and repossessed assets	$ 4,384	$ 5,297
Weighted Average [Member]
Fair Value Inputs Asset Quantitative Information [Line Items]
Impaired loans, Appraisal adjustments	0.00%	(4.80%)
Impaired loans, Liquidation expenses	0.00%	(7.60%)