LOANS, ALLOWANCE FOR LOAN LOSSES AND CREDIT QUALITY (Details Textual) - USD ($)		12 Months Ended
	Nov. 12, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans, Allowance for Loan Losses and Credit Quality [Abstract]
Days To Be Termed As Non Accrual Loans		90 days
Tdrs Recorded Investment On Nonaccrual Status		$ 1,993,000	$ 22,209,000
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, before Allowance for Credit Loss		13,540,590,000	9,371,470,000
Financing Receivable, Allowance for Credit Losses, Effect of Change in Method			(1,137,000)
Financing Receivable, Credit Loss, Expense (Reversal)		18,205,000	52,500,000	$ 6,000,000
Financing Receivable, Allowance for Credit Loss		146,922,000	113,392,000	67,740,000	$ 64,293,000
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Allowance for Credit Loss, Purchased with Credit Deterioration			1,157,000
Financing Receivable, Troubled Debt Restructuring, Subsequent Default		3,200,000	0	$ 0
Loans with active Deferrals		383,100,000	173,600,000
Credit Loss Status [Domain]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Credit Loss, Expense (Reversal)		32,500,000
US Government Insured Loan Program [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, before Allowance for Credit Loss		216,200,000	$ 791,900,000
Blue Hills Bancorp, Inc. [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Credit Loss, Expense (Reversal)	$ 50,700,000
Financing Receivable, Allowance for Credit Loss		$ 67,200,000