Fair Value Measurements - Schedule of Quantitative Information of Assets Measured at Fair Value on Nonrecurring Basis (Detail) - Level III [Member] - Impaired Loans [Member] $ in Thousands	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Valuation Technique, Discounted Cash Flow [Member]
Marketable Securities [Line Items]
Fair Value Estimate	$ 583	$ 551
Valuation Technique, Discounted Cash Flow [Member] | Minimum [Member] | Measurement Input, Discount Rate [Member]
Marketable Securities [Line Items]
Alternative investment, measurement input	3.5	4.4
Valuation Technique, Discounted Cash Flow [Member] | Maximum [Member] | Measurement Input, Discount Rate [Member]
Marketable Securities [Line Items]
Alternative investment, measurement input	7.5	7.5
Valuation Technique, Discounted Cash Flow [Member] | Weighted Average [Member] | Measurement Input, Discount Rate [Member]
Marketable Securities [Line Items]
Alternative investment, measurement input	5.1	5.3
Appraisal of Collateral [Member]
Marketable Securities [Line Items]
Fair Value Estimate	$ 33	$ 1,522
Alternative investment, measurement input	10	10
Appraisal of Collateral [Member] | Minimum [Member] | Measurement Input, Comparability Adjustment [Member]
Marketable Securities [Line Items]
Alternative investment, measurement input	25	6
Appraisal of Collateral [Member] | Maximum [Member] | Measurement Input, Comparability Adjustment [Member]
Marketable Securities [Line Items]
Alternative investment, measurement input	100	100
Appraisal of Collateral [Member] | Weighted Average [Member] | Measurement Input, Comparability Adjustment [Member]
Marketable Securities [Line Items]
Alternative investment, measurement input	85	7