Loans and Allowance for Credit Losses - Collateral Dependent Loans (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	$ 55,049
Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	26,598
Energy
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	21,755
Other Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	6,696
Real Estate | Construction and development
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	2,465
Real Estate | Construction and development | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	2,465
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	5,479
Real Estate | Single family residential | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	5,479
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	18,654
Real Estate | Other commercial | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	18,654
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	28,451
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	21,755
Commercial | Commercial | Other Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	$ 6,696