Fair Value of Financial Instruments - Information about Significant Unobservable Inputs (Level 3) Used in Valuation of Assets Measured at Fair Value on Nonrecurring Basis (Details) - Fair Value, Measurements, Nonrecurring - Significant Unobservable Inputs (Level 3) $ in Thousands	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Valuation of collateral | Minimum | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Discount rate	0.00	0.00
Valuation of collateral | Maximum | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Discount rate	0.30	0.30
Valuation of collateral | Impaired Loans
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value of assets	$ 3,997	$ 77,027
Appraised value of property less costs to sell | Minimum | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Discount rate	0.00	0.00
Appraised value of property less costs to sell | Maximum | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Discount rate	0.15	0.15
Appraised value of property less costs to sell | Other Real Estate Owned
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value of assets	$ 1,333	$ 13,174