LOANS AND ALLOWANCE FOR LOAN LOSSES (Loans Stated at Face Amount, Net of Unearned Income) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	$ 14,383,215		$ 12,610,936
Total Allowance for credit losses	(174,122)	$ (94,838)	(42,294)
Total loans held for investment, net	14,209,093		12,568,642
Construction and Land Development
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	1,207,190		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	2,107,333		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	3,497,929		3,286,098
Multifamily Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	731,582		633,743
Commercial and Industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	3,536,249		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	696,944		724,337
Residential 1-4 Family - Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	830,144		890,503
Residential 1-4 Family - Revolving
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	618,320		659,504
Auto
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	387,417		350,419
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	276,023		372,853
Other Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment, net of deferred fees and costs	494,084		$ 287,279
Paycheck Protection Program (PPP)
Loans and Leases Receivable Disclosure [Line Items]
Total loans held for investment, net	769,600
Paycheck Protection Program (PPP) | Commercial and Industrial
Loans and Leases Receivable Disclosure [Line Items]
Total loans held for investment, net	1,600,000
Paycheck Protection Program (PPP) | Other Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total loans held for investment, net	$ 21,300