GOODWILL AND OTHER INTANGIBLE ASSETS--Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended
	Aug. 30, 2019	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Goodwill		$ 937,771	$ 937,771	$ 937,771	$ 937,771
Other Depreciation and Amortization			2,800
Intangible assets amortization		$ 2,479	$ 2,792
Customer lists
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 39,400
Intangible assets amortization method		straight-line basis
Estimated weighted average life (in years)		11 years
Core deposits
Finite-Lived Intangible Assets [Line Items]
Intangible assets amortization method		accelerated basis
Estimated weighted average life (in years)		6 years 9 months 18 days