INVESTMENT SECURITIES - ACL on Debt Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning Balance			$ 1,310
Net charge-offs	$ 0
Ending Balance	1,157		1,157
MBS [Member]
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning Balance			1,002
Ending Balance	849		849
MBS [Member] | Private label [Member]
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning Balance			1,000
Net charge-offs	0
Ending Balance	800		800
Puerto Rico Government obligations [Member]
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Net charge-offs	0
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning Balance	1,166	$ 1,631	1,310	$ 0
Addtions for securities for which previous expected credit losses were recognized (provision for credit losses)	(9)	0	136	1,631
Net charge-offs		(245)	(17)	(245)
Ending Balance	1,157	1,386	1,157	1,386
Available-for-sale Securities [Member] | MBS [Member]
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Addtions for securities for which previous expected credit losses were recognized (provision for credit losses)	(9)
Net charge-offs		(245)		(245)
Available-for-sale Securities [Member] | MBS [Member] | Private label [Member]
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning Balance	858	1,323	1,002	0
Addtions for securities for which previous expected credit losses were recognized (provision for credit losses)		0	136	1,323
Net charge-offs			(17)
Ending Balance	849	1,078	849	1,078
Available-for-sale Securities [Member] | Puerto Rico Government obligations [Member]
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Beginning Balance	308	308	308	0
Addtions for securities for which previous expected credit losses were recognized (provision for credit losses)	0	0	0	308
Net charge-offs		0	0	0
Ending Balance	$ 308	$ 308	$ 308	$ 308