Loans and Allowance for Loan Losses - Impaired Loan Interest Income and Average Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable, Impaired [Line Items]
Total interest income recognized	$ 166	$ 1,122	$ 507	$ 2,227
Total average impaired loans	46,971	79,760	54,779	105,223
Commercial
Financing Receivable, Impaired [Line Items]
Total interest income recognized	27	781	88	1,564
Total average impaired loans	11,793	50,732	19,002	74,259
Energy
Financing Receivable, Impaired [Line Items]
Total interest income recognized	46	53	210	109
Total average impaired loans	16,798	12,534	17,527	13,850
Commercial real estate
Financing Receivable, Impaired [Line Items]
Total interest income recognized	58	278	135	532
Total average impaired loans	10,958	13,779	11,044	14,661
Construction and land development
Financing Receivable, Impaired [Line Items]
Total interest income recognized	0	0	0	1
Total average impaired loans	0	50	0	25
Residential real estate
Financing Receivable, Impaired [Line Items]
Total interest income recognized	35	10	74	21
Total average impaired loans	7,171	2,665	6,953	2,428
Consumer
Financing Receivable, Impaired [Line Items]
Total interest income recognized	0	0	0	0
Total average impaired loans	251	0	253	0
Paycheck Protection Program (“PPP”)
Financing Receivable, Impaired [Line Items]
Total interest income recognized	0	0	0	0
Total average impaired loans	$ 0	$ 0	$ 0	$ 0