CREDIT QUALITY ASSESSMENT (Summary information on the allowance for credit loss activity) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period			$ 56,132	$ 53,486	$ 53,486
Initial allowance on acquired Revere PCD loans			18,628	0
Provision (credit)	$ 58,686	$ 1,633	83,155	1,505	4,684
Loan charge-offs			(1,039)	(1,197)	(2,668)
Loan recoveries			860	230	630
Net recoveries (charge-offs)			(179)	(967)	(2,038)
Balance at end of period	$ 163,481	$ 54,024	163,481	54,024	56,132
Initial allowance on purchased credit deteriorated loans at adoption of ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period			2,762	0	0
Balance at end of period					2,762
Transition impact of adopting ASC 326 [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Balance at beginning of period			$ 2,983	$ 0	0
Balance at end of period					$ 2,983