Fair Value Measurements - Summary of Quantitative Fair Value Measurements for Level 3 (Detail) - Fair Value, Inputs, Level 3 $ in Thousands	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Impaired loans	$ 4,657	$ 3,491
Other real estate owned	$ 3,501	$ 4,284
Impaired Loans | Minimum | Discounted Appraised Value | Selling Cost
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Impaired loans	0	6
Impaired Loans | Minimum | Discounted Appraised Value | Lack of Marketability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Impaired loans	50	50
Impaired Loans | Minimum | Discounted Cash Flows | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Impaired loans	5	5
Impaired Loans | Maximum | Discounted Appraised Value | Selling Cost
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Impaired loans	30	20
Impaired Loans | Maximum | Discounted Appraised Value | Lack of Marketability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Impaired loans	100	90
Impaired Loans | Maximum | Discounted Cash Flows | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Impaired loans	6	6
Impaired Loans | Weighted Average | Discounted Appraised Value | Selling Cost
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Impaired loans	18	16
Impaired Loans | Weighted Average | Discounted Appraised Value | Lack of Marketability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Impaired loans	70	65
Impaired Loans | Weighted Average | Discounted Cash Flows | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Impaired loans	6	6
Other Real Estate Owned | Minimum | Discounted Appraised Value | Selling Cost
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Other real estate owned	3	3
Other Real Estate Owned | Minimum | Discounted Appraised Value | Lack of Marketability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Other real estate owned	4	10
Other Real Estate Owned | Maximum | Discounted Appraised Value | Selling Cost
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Other real estate owned	13	13
Other Real Estate Owned | Maximum | Discounted Appraised Value | Lack of Marketability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Other real estate owned	100	100
Other Real Estate Owned | Weighted Average | Discounted Appraised Value | Selling Cost
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Other real estate owned	4	8
Other Real Estate Owned | Weighted Average | Discounted Appraised Value | Lack of Marketability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Unobservable Input, Other real estate owned	12	16