GOODWILL AND OTHER INTANGIBLE ASSETS (Gross Carrying Amouns and Accumulated Amortization of Intangible Assets and Goodwill) (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 42,944,000	$ 12,156,000
Accumulated Amortization	(6,801,000)	(4,315,000)
Net Carrying Amount	36,143,000	7,841,000
Goodwill Gross Carrying Amount	370,547,000	347,149,000
Goodwill, Net Carrying Amount	370,547,000	347,149,000
Core deposits [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	29,038,000	10,678,000
Accumulated Amortization	(5,399,000)	(3,689,000)
Net Carrying Amount	$ 23,639,000	$ 6,989,000
Weighted average useful life	9 years	8 years
Core deposits [Member] | Revere acquisition [Member]
Finite Lived Intangible Assets [Line Items]
Weighted average useful life	9 years 8 months 1 day
Intangible asset acquired	$ 18,400,000
Other Identifiable Intangible Assets
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	13,906,000	$ 1,478,000
Accumulated Amortization	(1,402,000)	(626,000)
Net Carrying Amount	$ 12,504,000	$ 852,000
Weighted average useful life	11 years 2 months 12 days	9 years 8 months 12 days