Loans and Allowance for Loan Losses ("ALLL") - Impaired Loan Interest Income and Average Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Impaired [Line Items]
Total interest income recognized	$ 108	$ 692	$ 1,552	$ 1,816
Total average impaired loans	91,482	87,261	97,447	83,238
Commercial
Financing Receivable, Impaired [Line Items]
Total interest income recognized	12	386	841	862
Total average impaired loans	45,482	54,410	49,538	49,265
Energy
Financing Receivable, Impaired [Line Items]
Total interest income recognized	2	98	257	324
Total average impaired loans	21,396	13,623	23,220	15,091
Commercial real estate
Financing Receivable, Impaired [Line Items]
Total interest income recognized	58	200	346	613
Total average impaired loans	17,937	16,690	18,132	16,528
Construction and land development
Financing Receivable, Impaired [Line Items]
Total interest income recognized	0	0	0	0
Total average impaired loans	0	0	0	0
Residential real estate
Financing Receivable, Impaired [Line Items]
Total interest income recognized	36	8	108	17
Total average impaired loans	6,419	2,538	6,304	2,354
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
Consumer
Financing Receivable, Impaired [Line Items]
Total interest income recognized	0	0	0	0
Total average impaired loans	$ 248	$ 0	$ 253	$ 0