Loans Held for Investment and Allowance for Loan Losses - Collateral Dependent (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Financing Receivable, Past Due [Line Items]
Collateral-dependent Loans	$ 96,276
Business Assets
Financing Receivable, Past Due [Line Items]
Collateral-dependent Loans	11,946
Energy Collateral
Financing Receivable, Past Due [Line Items]
Collateral-dependent Loans	84,330
Commercial
Financing Receivable, Past Due [Line Items]
Collateral-dependent Loans	11,946
Commercial | Business Assets
Financing Receivable, Past Due [Line Items]
Collateral-dependent Loans	11,946
Commercial | Energy Collateral
Financing Receivable, Past Due [Line Items]
Collateral-dependent Loans	0
Energy
Financing Receivable, Past Due [Line Items]
Collateral-dependent Loans	84,330
Energy | Business Assets
Financing Receivable, Past Due [Line Items]
Collateral-dependent Loans	0
Energy | Energy Collateral
Financing Receivable, Past Due [Line Items]
Collateral-dependent Loans	$ 84,330