LEASES - Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Components of lease expense:
Operating lease cost (resulting from lease payments)	$ 3,047	$ 3,154	$ 9,333	$ 9,281
Supplemental cash flow information related to leases:
Operating cash flows from operating leases	3,208	4,158	9,762	10,160
ROU assets obtained in the exchange for lease liabilities due to new leases and acquisitions	0	0	803	0
Supplemental balance sheet information related to leases:
Operating lease ROU assets	59,597		59,597		$ 65,215
Lease liability	$ 69,060		$ 69,060		$ 74,982
Other information related to leases:
Weighted average remaining lease term of operating leases	9 years 1 month 6 days		9 years 1 month 6 days		9 years 6 months
Weighted average discount rate of operating leases	2.92%		2.92%		3.04%
Revere Bank And RPJ
Supplemental cash flow information related to leases:
ROU assets obtained in the exchange for lease liabilities due to new leases and acquisitions	$ 0	$ 0	$ 0	$ 7,720