Loans and Allowance for Loan Losses ("ALLL") - Loan Aging Analysis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 46,755	$ 44,832
Current	4,199,429	4,410,268
Total Loans Receivable	4,246,184	4,455,100
Loans >= 90 Days and Accruing	342	1,024
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	3,072	10,137
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	34,528	7,941
90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	9,155	26,754
Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	15,583	19,997
Current	1,289,953	1,318,760
Total Loans Receivable	1,305,536	1,338,757
Loans >= 90 Days and Accruing	300	0
Commercial | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,716	8,497
Commercial | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	12,700	264
Commercial | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	1,167	11,236
Energy
Financing Receivable, Past Due [Line Items]
Total Past Due	13,382	7,173
Current	282,983	338,060
Total Loans Receivable	296,365	345,233
Loans >= 90 Days and Accruing	0	372
Energy | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	738	0
Energy | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	6,500	0
Energy | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	6,144	7,173
Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	15,726	12,565
Current	1,250,968	1,166,969
Total Loans Receivable	1,266,694	1,179,534
Loans >= 90 Days and Accruing	0	0
Commercial real estate | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	398	63
Commercial real estate | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	15,328	7,677
Commercial real estate | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	0	4,825
Construction and land development
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Current	585,134	563,144
Total Loans Receivable	585,134	563,144
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	0
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	2,035	5,097
Current	618,842	675,835
Total Loans Receivable	620,877	680,932
Loans >= 90 Days and Accruing	42	652
Residential real estate | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	191	1,577
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	1,844	3,520
Paycheck Protection Program ("PPP")
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Current	109,465	292,230
Total Loans Receivable	109,465	292,230
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	29	0
Current	62,084	55,270
Total Loans Receivable	62,113	55,270
Loans >= 90 Days and Accruing	0	0
Consumer | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	29	0
Consumer | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Consumer | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 0	$ 0