Fair Value Measurements - Fair Value of Assets on a Nonrecurring Basis (Details) - Nonrecurring - Significant Unobservable Inputs (Level 3) $ in Thousands	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	$ 74,980	$ 73,518
Impaired loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	73,137	70,619
Other real estate and repossessed assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	$ 1,843	$ 2,899
Discount rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired originated loans, measurement input	0.20
Other real estate assets, measurement input	0.20
Discount rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired originated loans, measurement input	0.30
Other real estate assets, measurement input	0.30