PREMISES AND EQUIPMENT (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment, Net [Abstract]
Premises and equipment, gross	$ 312,434	$ 297,920
Accumulated depreciation	(146,779)	(133,282)
Premises and equipment, net	165,655	164,638
Land and Land Improvements [Member]
Property, Plant and Equipment, Net [Abstract]
Premises and equipment, gross	29,070	26,301
Bank Premises [Member]
Property, Plant and Equipment, Net [Abstract]
Premises and equipment, gross	149,217	141,905
Equipment and Construction in Progress [Member]
Property, Plant and Equipment, Net [Abstract]
Premises and equipment, gross	99,239	89,819
Operating Lease Right-of-Use Assets [Member]
Property, Plant and Equipment, Net [Abstract]
Premises and equipment, gross	$ 34,908	$ 39,895