Loans and Allowance for Loan Losses - Non-Accrual Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	$ 37,534	$ 39,675
Commercial
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	10,966	32,130
Energy
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	15,384	4,540
Commercial real estate
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	7,000	1,063
Construction and land development
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	0	0
Residential real estate
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	3,935	1,942
Consumer
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	249	0
Paycheck Protection Program (“PPP”)
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	$ 0	$ 0