GOODWILL AND OTHER INTANGIBLE ASSETS--Schedule of Other Intangibles (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 96,891	$ 100,564
Finite-Lived Intangible Assets, Accumulated Amortization	(40,080)	(36,012)
Core deposits
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	47,325	51,031
Finite-Lived Intangible Assets, Accumulated Amortization	(27,748)	(27,524)
Customer lists
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	39,420	39,420
Finite-Lived Intangible Assets, Accumulated Amortization	(7,466)	(4,778)
Other
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	10,146	10,113
Finite-Lived Intangible Assets, Accumulated Amortization	$ (4,866)	$ (3,710)