PREMISES, FURNITURE AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total	$ 324,100	$ 302,899
Less accumulated depreciation	(104,505)	(105,341)
Premises, furniture and equipment, net	219,595	197,558
Depreciation expense	11,800	12,000	$ 11,700
Land and land improvements
Property, Plant and Equipment [Line Items]
Total	61,930	60,444
Buildings and building improvements
Property, Plant and Equipment [Line Items]
Total	192,702	176,838
Depreciation expense	6,500	6,200	5,800
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total	69,468	65,617
Depreciation expense	$ 5,300	$ 5,800	$ 6,000