Loans and Allowance for Loan Losses - Internal Risk Ratings (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	$ 4,429,241	$ 3,861,707
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	4,021,662	3,727,182
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	170,450	47,629
Substandard | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	199,595	47,221
Substandard | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	29,030	34,192
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	8,504	5,483
Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	1,284,919	1,356,817
Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	1,143,316	1,258,952
Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	53,411	27,069
Commercial | Substandard | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	77,226	38,666
Commercial | Substandard | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	7,662	32,130
Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	3,304	0
Commercial | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Energy
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	390,346	408,573
Energy | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	210,557	392,233
Energy | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	71,837	9,460
Energy | Substandard | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	92,568	2,340
Energy | Substandard | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	10,997	0
Energy | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	4,387	4,540
Energy | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	1,141,277	1,024,041
Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	1,069,590	1,007,921
Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	39,332	9,311
Commercial real estate | Substandard | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	25,355	5,746
Commercial real estate | Substandard | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	6,187	120
Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	813	943
Commercial real estate | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Construction and land development
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	661,691	628,418
Construction and land development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	655,200	628,418
Construction and land development | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	5,330	0
Construction and land development | Substandard | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	1,161	0
Construction and land development | Substandard | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Construction and land development | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Construction and land development | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	536,270	398,695
Residential real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	528,510	394,495
Residential real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	540	1,789
Residential real estate | Substandard | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	3,285	469
Residential real estate | Substandard | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	3,935	1,942
Residential real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Residential real estate | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Paycheck Protection Program (“PPP”)
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	369,022	0
Paycheck Protection Program (“PPP”) | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	369,022	0
Paycheck Protection Program (“PPP”) | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Paycheck Protection Program (“PPP”) | Substandard | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Paycheck Protection Program (“PPP”) | Substandard | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Paycheck Protection Program (“PPP”) | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Paycheck Protection Program (“PPP”) | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	45,716	45,163
Consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	45,467	45,163
Consumer | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Consumer | Substandard | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Consumer | Substandard | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	249	0
Consumer | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	0	0
Consumer | Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Gross loans	$ 0	$ 0