Loans and Allowance for Loan Losses ("ALLL") - Troubled Debt Restructuring Loans (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	$ 0	$ 0	$ 5,576	$ 34,766
Number of Loans | contract			14		12
Outstanding Balance	19,198		$ 19,198		$ 39,543
Balance 90 days past due at any time during previous 12 months			6,520		831
Increase in allowance for loan losses from loan restructuring			$ 3,000		$ 18,000
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | contract			6		7
Outstanding Balance	7,895		$ 7,895		$ 31,770
Balance 90 days past due at any time during previous 12 months			$ 3,762		$ 831
Energy
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | contract			3		2
Outstanding Balance	3,373		$ 3,373		$ 2,864
Balance 90 days past due at any time during previous 12 months			$ 2,713		$ 0
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | contract			3		3
Outstanding Balance	4,683		$ 4,683		$ 4,909
Balance 90 days past due at any time during previous 12 months			$ 0		$ 0
Construction and land development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | contract			0		0
Outstanding Balance	0		$ 0		$ 0
Balance 90 days past due at any time during previous 12 months			$ 0		$ 0
Residential real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | contract			2		0
Outstanding Balance	3,247		$ 3,247		$ 0
Balance 90 days past due at any time during previous 12 months			$ 45		$ 0
Paycheck Protection Program (“PPP”)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | contract			0		0
Outstanding Balance	0		$ 0		$ 0
Balance 90 days past due at any time during previous 12 months			$ 0		$ 0
Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | contract			0		0
Outstanding Balance	0		$ 0		$ 0
Balance 90 days past due at any time during previous 12 months			0		$ 0
Interest Rate Reduction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	0	0	3,171	0
Reduction of Monthly Payment | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	0	0	0	994
Reduction of Monthly Payment | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	0	0	0	3,767
Extension of Maturity Date | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	0	0	0	30,005
Extension of Maturity Date | Energy
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	0	0	2,340	0
Payment Deferral | Residential real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	$ 0	$ 0	$ 65	$ 0