CREDIT QUALITY ASSESSMENT - Allowance for credit loss activity (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 01, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				$ 56,132	$ 53,486	$ 53,486
Initial allowance on acquired Revere PCD loans	$ 18,600			18,628	0
Provision for credit losses		$ 7,003	$ 1,524	90,158	3,029	4,684
Loan charge-offs				(1,255)	(2,101)	(2,668)
Loan recoveries				906	578	630
Net charge-offs				(349)	(1,523)	(2,038)
Balance at period end		170,314	$ 54,992	170,314	54,992	56,132
Initial allowance on PCD loans at adoption of ASC 326
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				2,762	0	0
Balance at period end		$ 2,762		2,762		2,762
Transition impact of adopting ASC 326
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				$ 2,983	$ 0	0
Balance at period end						$ 2,983