Loans and Allowance for Loan Losses ("ALLL") - Non-Accrual Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	$ 75,560	$ 39,675
Commercial
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	37,774	32,130
Energy
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	21,185	4,540
Commercial real estate
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	13,176	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	3,179	1,942
Paycheck Protection Program (“PPP”)
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	0	0
Consumer
Financing Receivable, Nonaccrual [Line Items]
Total non-accrual loans	$ 246	$ 0