BANK PREMISES AND EQUIPMENT (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total cost		$ 216,476	$ 218,921
Accumulated depreciation		(100,083)	(95,247)
Net bank premises and equipment		116,393	123,674
Depreciation expense		12,800	11,400	$ 9,100
Rental Income, Nonoperating	$ 1,600	1,500
Land [Member]
Property, Plant and Equipment [Line Items]
Total cost		32,450	32,619
Bank Premises [Member]
Property, Plant and Equipment [Line Items]
Total cost		$ 63,544	62,455
Bank Premises [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		5 years
Bank Premises [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		40 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total cost		$ 38,667	35,498
Leasehold Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		1 year
Leasehold Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		27 years
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total cost		$ 81,815	77,705
Furniture and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		2 years
Furniture and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		12 years
Equipment Leased to Other Party [Member]
Property, Plant and Equipment [Line Items]
Total cost		$ 10,600	$ 10,644
Equipment Leased to Other Party [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives		7 years