Loans and Allowance for Loan Losses - Loan Aging Analysis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 55,032	$ 48,834
Current	4,374,209	3,812,873
Total Loans Receivable	4,429,241	3,861,707
Loans >= 90 Days and Accruing	220	4,591
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	14,205	6,292
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	20,676	530
90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	20,151	42,012
Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	15,351	32,278
Current	1,269,568	1,324,539
Total Loans Receivable	1,284,919	1,356,817
Loans >= 90 Days and Accruing	0	37
Commercial | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	4,645	1,091
Commercial | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	3,391	276
Commercial | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	7,315	30,911
Energy
Financing Receivable, Past Due [Line Items]
Total Past Due	21,358	6,933
Current	368,988	401,640
Total Loans Receivable	390,346	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	16,918	0
Energy | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	4,440	4,593
Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	12,720	4,905
Current	1,128,557	1,019,136
Total Loans Receivable	1,141,277	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	8,009	316
Commercial real estate | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	230	0
Commercial real estate | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	4,481	4,589
Construction and land development
Financing Receivable, Past Due [Line Items]
Total Past Due	194	196
Current	661,497	628,222
Total Loans Receivable	661,691	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	194	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	5,272	4,266
Current	530,998	394,429
Total Loans Receivable	536,270	398,695
Loans >= 90 Days and Accruing	220	0
Residential real estate | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,357	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	3,915	1,919
Paycheck Protection Program (“PPP”)
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Current	369,022	0
Total Loans Receivable	369,022	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	137	256
Current	45,579	44,907
Total Loans Receivable	45,716	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	137	254
Consumer | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 0	$ 0