Loans and Allowance for Loan Leases - Non-Accrual Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	$ 26,255	$ 39,675
Commercial
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	10,352	32,130
Energy
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	8,265	4,540
Commercial real estate
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	5,443	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	1,941	1,942
Consumer
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	$ 254	$ 0