Loans and Allowance for Credit Losses - Collateral Dependent Loans (Details) $ in Thousands	Jun. 30, 2021 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	$ 74,815
Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	40,159
Energy
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	30,677
Other Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	3,979
Real Estate | Construction and development
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	2,788
Real Estate | Construction and development | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	2,788
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	2,940
Real Estate | Single family residential | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	2,940
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	34,431
Real Estate | Other commercial | Real Estate Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	34,431
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	34,656
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	30,677
Commercial | Commercial | Other Collateral
Loans and Leases Receivable Disclosure [Line Items]
Financing receivable, collateral dependent, amount	$ 3,979