LOANS AND ALLOWANCE FOR LOAN LOSSES (Loans Stated at Face Amount, Net of Unearned Income) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	$ 14,021,314		$ 12,610,936
Total Allowance for credit losses	(160,540)	$ (94,838)	(42,294)
Total loans held for investment, net	13,860,774		12,568,642
Loans receivable, deferred fees and costs	69,700		69,800
Construction and Land Development
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	925,798		1,250,924
Commercial Real Estate - Owner Occupied
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	2,128,909		2,041,243
Commercial Real Estate - Non-Owner Occupied
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	3,657,562		3,286,098
Multifamily Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	814,745		633,743
Commercial and Industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	3,263,460		2,114,033
Residential 1-4 Family - Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	671,949		724,337
Residential 1-4 Family - Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	822,866		890,503
Residential 1-4 Family - Revolving
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	596,996		659,504
Auto
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	401,324		350,419
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	247,730		372,853
Other Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	489,975		$ 287,279
Paycheck Protection Program (PPP) | Commercial and Industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans held for investment, net	1,200,000
Paycheck Protection Program (PPP) | Other Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans held for investment, net	$ 11,300