Fair Value - Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Non-recurring basis
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Impaired loans - held-for-investment, Fair Value	$ 7,152	$ 361
Non-recurring basis | Significant Unobservable Inputs (Level 3)
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Impaired loans - held-for-investment, Fair Value	$ 7,152	361
Commercial | Non-recurring basis | Significant Unobservable Inputs (Level 3) | Market Approach
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Impaired loans - held-for-investment, Fair Value		$ 242
Commercial | Non-recurring basis | Significant Unobservable Inputs (Level 3) | Market Approach | Maximum
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Discount adjustment for differences between comparable sales (as a percent)	1.00%	1.00%
Commercial | Commercial | Significant Unobservable Inputs (Level 3) | Market Approach
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Impaired loans - held-for-investment, Fair Value	$ 7,152
Commercial | Commercial | Non-recurring basis
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Impaired loans - held-for-investment, Fair Value	7,152	$ 242
Commercial | Commercial | Non-recurring basis | Significant Unobservable Inputs (Level 3)
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Impaired loans - held-for-investment, Fair Value	$ 7,152	242
Land and construction | Real estate | Non-recurring basis
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Impaired loans - held-for-investment, Fair Value		119
Land and construction | Real estate | Non-recurring basis | Significant Unobservable Inputs (Level 3)
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Impaired loans - held-for-investment, Fair Value		119
Land and construction | Real estate | Non-recurring basis | Significant Unobservable Inputs (Level 3) | Market Approach
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Impaired loans - held-for-investment, Fair Value		$ 119
Land and construction | Real estate | Non-recurring basis | Significant Unobservable Inputs (Level 3) | Market Approach | Maximum
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value on a non-recurring basis
Discount adjustment for differences between comparable sales (as a percent)		1.00%