GOODWILL AND OTHER INTANGIBLE ASSETS (Gross Carrying Amouns and Accumulated Amortization of Intangible Assets and Goodwill) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 24,584,000	$ 12,156,000
Accumulated Amortization	(4,803,000)	(4,315,000)
Net Carrying Amount	19,781,000	7,841,000
Goodwill Gross Carrying Amount	369,708,000	347,149,000
Goodwill, Net Carrying Amount	369,708,000	347,149,000
Core deposits [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	10,678,000	10,678,000
Accumulated Amortization	(4,077,000)	(3,689,000)
Net Carrying Amount	$ 6,601,000	$ 6,989,000
Finite-Lived Intangible Asset, Useful Life	7 years 9 months 18 days	8 years
Other Identifiable Intangible Assets
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 13,906,000	$ 1,478,000
Accumulated Amortization	(726,000)	(626,000)
Net Carrying Amount	$ 13,180,000	$ 852,000
Finite-Lived Intangible Asset, Useful Life	11 years 4 months 24 days	9 years 8 months 12 days