Fair Value Measurements - 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) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Valuation of collateral | Minimum
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rate	0.00%	0.00%
Valuation of collateral | Maximum
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rate	30.00%	30.00%
Valuation of collateral | Impaired Loans
Fair Value Inputs Assets Quantitative Information [Line Items]
Fair value of assets	$ 431	$ 77,027
Appraised value of property less costs to sell | Minimum
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rate	0.00%	0.00%
Appraised value of property less costs to sell | Maximum
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rate	15.00%	15.00%
Appraised value of property less costs to sell | Other Real Estate Owned
Fair Value Inputs Assets Quantitative Information [Line Items]
Fair value of assets	$ 798	$ 13,174