Fair Value Measurements Fair Value Measurement, Measured On Non-Recurring Basis, Signfiicant Unobservable Inputs, Quantitative Information (Details) - Fair Value, Measurements, Nonrecurring [Member] - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Impaired Loans [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		$ 9,712		$ 410
Real estate and other repossessed assets [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		144		$ 7,094
Discounted Cash Flow [Member] | Impaired Loans [Member] | Fair Value, Inputs, Level 3 [Member] | Management knowledge of Industry [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		9,712
Discounted Cash Flow [Member] | Impaired Loans [Member] | Fair Value, Inputs, Level 3 [Member] | Recoverable oil and gas reserves, forward-looking commodity prices, and estimated operating costs [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure			$ 17,401
Discounted Cash Flow [Member] | Real estate and other repossessed assets [Member] | Fair Value, Inputs, Level 3 [Member] | Recoverable oil and gas reserves, forward-looking commodity prices, and estimated operating costs [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, Fair Value Disclosure		$ 144	$ 6,366
Minimum [Member] | Impaired Loans [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value of Impaired Loans as Percentage of Unpaid Principal Balance	[1]	14.00%	35.00%
Minimum [Member] | Real estate and other repossessed assets [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurement, Percentage of Appraised Value. Minimum		75.00%
Maximum [Member] | Impaired Loans [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value of Impaired Loans as Percentage of Unpaid Principal Balance	[1]	74.00%	80.00%
Maximum [Member] | Real estate and other repossessed assets [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurement, Percentage of Appraised Value. Minimum		85.00%
Weighted Average [Member] | Impaired Loans [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value of Impaired Loans as Percentage of Unpaid Principal Balance	[1]	31.00%	50.00%
Weighted Average [Member] | Real estate and other repossessed assets [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Measurement, Percentage of Appraised Value. Minimum		79.00%

[1] Represents fair value as a percentage of the unpaid principal balance.