Loans and Allowance for Credit Losses - Collateral Dependent Loans (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	$ 69,998
Real Estate Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	23,554
Energy
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	40,703
Other Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	5,741
Real Estate | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	1,539
Real Estate | Construction and development | Real Estate Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	1,539
Real Estate | Construction and development | Energy
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Construction and development | Other Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	6,950
Real Estate | Single family residential | Real Estate Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	6,950
Real Estate | Single family residential | Energy
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Single family residential | Other Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	46,444
Real Estate | Other commercial | Real Estate Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	0
Real Estate | Other commercial | Energy
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	40,703
Real Estate | Other commercial | Other Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	5,741
Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	15,065
Commercial | Commercial | Real Estate Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	15,065
Commercial | Commercial | Energy
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	0
Commercial | Commercial | Other Collateral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, collateral dependent, amount	$ 0