Loans and Allowance for Loan Losses - Collateral Dependent Loans (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	$ 75,670
Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	23,648
Energy
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	43,573
Other Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	8,449
Real Estate | Construction and development
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	3,078
Real Estate | Construction and development | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	3,078
Real Estate | Construction and development | Energy
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Construction and development | Other Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Single family residential
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	3,586
Real Estate | Single family residential | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	3,586
Real Estate | Single family residential | Energy
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Single family residential | Other Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Other commercial
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	16,984
Real Estate | Other commercial | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	16,984
Real Estate | Other commercial | Energy
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Other commercial | Other Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	0
Commercial | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	52,022
Commercial | Commercial | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	0
Commercial | Commercial | Energy
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	43,573
Commercial | Commercial | Other Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	$ 8,449