LEASES Textual (Details)	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	5 years 8 months 19 days	5 years 7 months 2 days	6 years 5 months 4 days
Operating Lease, Weighted Average Discount Rate, Percent	1.97%	2.13%	2.75%
Operating Lease, Right-of-Use Asset	$ 60,200,000	$ 49,700,000		$ 32,800,000
Operating Lease, Impairment Loss	$ 0	4,163,000	$ 0
Property Subject to or Available for Operating Lease, Number of Units	126
Operating Lease, Impairment Loss	$ 0	$ 4,163,000	$ 0
Blue Hills Bancorp, Inc. [Member]
Lessee, Lease, Description [Line Items]
Business Acquisition, Operating Lease Impairment Charge	$ 2,300,000
Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Renewal Term	20 years
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Renewal Term	3 years