GOODWILL AND OTHER INTANGIBLE ASSETS - Gross Carrying Amounts and Accumulated Amortization of Intangible Assets and Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 42,944	$ 12,156
Accumulated Amortization	(10,423)	(4,315)
Net Carrying Amount	32,521	7,841
Goodwill	370,223	347,149
Goodwill	370,223	347,149	$ 347,149
Core deposit intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	29,038	10,678
Accumulated Amortization	(7,969)	(3,689)
Net Carrying Amount	$ 21,069	$ 6,989
Core deposit intangibles | Weighted Average
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	8 years 4 months 24 days	8 years
Other identifiable intangibles
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 13,906	$ 1,478
Accumulated Amortization	(2,454)	(626)
Net Carrying Amount	$ 11,452	$ 852
Other identifiable intangibles | Weighted Average
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	10 years 8 months 12 days	9 years 8 months 12 days