Loans and Allowance for Loan Losses ("ALLL") - Loan Loss Activity - Previous GAAP (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	$ 74,551	$ 75,295
Provision	3,500	11,000
Charge-offs	(2,566)	(10,832)
Recoveries	8	30
Ending balance	75,493	75,493
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	23,464	24,693
Provision	7,532	14,547
Charge-offs	(2,566)	(10,832)
Recoveries	3	25
Ending balance	28,433	28,433
Energy
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	20,292	18,341
Provision	(2,443)	(492)
Charge-offs	0	0
Recoveries	0	0
Ending balance	17,849	17,849
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	20,609	22,354
Provision	(1,428)	(3,173)
Charge-offs	0	0
Recoveries	0	0
Ending balance	19,181	19,181
Construction and land development
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	3,837	3,612
Provision	48	273
Charge-offs	0	0
Recoveries	0	0
Ending balance	3,885	3,885
Residential and Multifamily Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	6,056	5,842
Provision	(230)	(16)
Charge-offs	0	0
Recoveries	0	0
Ending balance	5,826	5,826
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	293	453
Provision	21	(139)
Charge-offs	0	0
Recoveries	5	5
Ending balance	$ 319	$ 319