Loans and Allowance for Loan Losses ("ALLL") - Loan Aging Analysis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 65,646	$ 48,834
Current	4,427,468	3,812,873
Total Loans Receivable	4,493,114	3,861,707
Loans >= 90 Days and Accruing	4,324	4,591
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	15,324	6,292
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	30,027	530
90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	20,295	42,012
Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	47,402	32,278
Current	1,244,170	1,324,539
Total Loans Receivable	1,291,572	1,356,817
Loans >= 90 Days and Accruing	1,141	37
Commercial | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	12,274	1,091
Commercial | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	28,487	276
Commercial | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	6,641	30,911
Energy
Financing Receivable, Past Due [Line Items]
Total Past Due	4,595	6,933
Current	379,586	401,640
Total Loans Receivable	384,181	408,573
Loans >= 90 Days and Accruing	0	53
Energy | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	2,340
Energy | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,540	0
Energy | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	3,055	4,593
Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	5,934	4,905
Current	1,189,697	1,019,136
Total Loans Receivable	1,195,631	1,024,041
Loans >= 90 Days and Accruing	0	4,501
Commercial real estate | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,459	316
Commercial real estate | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Commercial real estate | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	4,475	4,589
Construction and land development
Financing Receivable, Past Due [Line Items]
Total Past Due	0	196
Current	587,617	628,222
Total Loans Receivable	587,617	628,418
Loans >= 90 Days and Accruing	0	0
Construction and land development | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	196
Construction and land development | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Construction and land development | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Residential real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	7,715	4,266
Current	610,367	394,429
Total Loans Receivable	618,082	398,695
Loans >= 90 Days and Accruing	3,183	0
Residential real estate | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,591	2,347
Residential real estate | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Residential real estate | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	6,124	1,919
Paycheck Protection Program (“PPP”)
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Current	369,260	0
Total Loans Receivable	369,260	0
Loans >= 90 Days and Accruing	0	0
Paycheck Protection Program (“PPP”) | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Paycheck Protection Program (“PPP”) | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Paycheck Protection Program (“PPP”) | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	0	256
Current	46,771	44,907
Total Loans Receivable	46,771	45,163
Loans >= 90 Days and Accruing	0	0
Consumer | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	2
Consumer | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	254
Consumer | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 0	$ 0