Fair Value - Summary of Quantitative Information About Level 3 Fair Value Measurements for Assets Measured at Fair Value on a Non-Recurring Basis (Details) - Fair Value, Measurements, Nonrecurring [Member] $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commercial and industrial
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	$ 2,719	$ 1,388
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unobservable Input(s)	Loss severity
Significant Unobservable Inputs (Level 3) | Measurement Input, Discount Rate | Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique(s)	5%
Significant Unobservable Inputs (Level 3) | Measurement Input, Discount Rate | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique(s)	50%
Significant Unobservable Inputs (Level 3) | Commercial and industrial
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	$ 2,719	$ 1,388
Valuation Technique(s)	Discounted cash flow	Dec. 31, 2017: Sales comparison approach
Unobservable Input(s)	Probability of default	Dec. 31, 2017:Appraisal discounts
Range (Weighted-Average)		0.15
Significant Unobservable Inputs (Level 3) | Commercial and industrial | Measurement Input, Discount Rate | Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique(s)	5%
Significant Unobservable Inputs (Level 3) | Commercial and industrial | Measurement Input, Discount Rate | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique(s)	60%