Loans and Allowance for Loan Losses ("ALLL") - Loan Loss Activity - Previous GAAP (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	$ 75,493	$ 75,295
Provision	(10,000)	1,000
Charge-offs	(1,575)	(12,407)
Recoveries	234	264
Ending balance	64,152	64,152
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	28,433	24,693
Provision	(3,666)	10,881
Charge-offs	(1,071)	(11,903)
Recoveries	225	250
Ending balance	23,921	23,921
Energy
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	17,849	18,341
Provision	(4,798)	(5,290)
Charge-offs	(503)	(503)
Recoveries	0	0
Ending balance	12,548	12,548
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	19,181	22,354
Provision	(236)	(3,409)
Charge-offs	0	0
Recoveries	0	0
Ending balance	18,945	18,945
Construction and land development
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	3,885	3,612
Provision	(694)	(421)
Charge-offs	0	0
Recoveries	0	0
Ending balance	3,191	3,191
Residential and Multifamily Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	5,826	5,842
Provision	(561)	(577)
Charge-offs	0	0
Recoveries	5	5
Ending balance	5,270	5,270
Paycheck Protection Program ("PPP")
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	0	0
Provision	0	0
Charge-offs	0	0
Recoveries	0	0
Ending balance	0	0
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	319	453
Provision	(45)	(184)
Charge-offs	(1)	(1)
Recoveries	4	9
Ending balance	$ 277	$ 277