LOANS HELD FOR INVESTMENT - Additional Information (Detail) $ in Thousands		9 Months Ended
	Jun. 30, 2020 USD ($) numberofcontracts	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		$ 469,078		$ 508,378
Loans and Leases Receivable, Gross		$ 11,800,000
Minimum Period To Be Considered For Loan To Have Defaulted		90 days
TDR [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring	$ 496,207	$ 488,615	$ 495,838	487,997	$ 582,389	$ 582,647
Outstanding unfunded commitments on TDR loans		$ 5,000
Loan Restructuring Trial Modifications Period		6 months
Payment Deferral [Member] | COVID-19
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		$ 1,200,000
Financing Receivable Deferral Payment Number Of Agreements | numberofcontracts	25,173
United States [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		25,898		19,499
Performing Financing Receivable [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring		399,700		398,300
Performing Financing Receivable [Member] | Ab Note Restructure Workout Strategy [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring		41,600
Performing Financing Receivable [Member] | United States [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring		$ 9,500		9,900
Collateral Pledged [Member] | Weighted Average [Member]
Loans and Leases Receivable Disclosure [Line Items]
LTV Coverage %		84.00%
Loans held for investment [Member] | Payment Deferral [Member] | COVID-19
Loans and Leases Receivable Disclosure [Line Items]
Credit risk concentration		10.00%
Loans held for investment [Member] | Puerto Rico [Member]
Loans and Leases Receivable Disclosure [Line Items]
Credit risk concentration		79.00%
Loans held for investment [Member] | United States [Member]
Loans and Leases Receivable Disclosure [Line Items]
Credit risk concentration		17.00%
Loans held for investment [Member] | USVI and BVI [Member]
Loans and Leases Receivable Disclosure [Line Items]
Credit risk concentration		4.00%
Residential Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Residential mortgage loans in process of foreclosure		$ 177,800
Financing Receivable, Real Estate Acquired Through Foreclosure [Policy Text Block]		The Corporation commences the foreclosure process on residential real estate loans when a borrower becomes 120 days delinquent in accordance with the requirements of the Consumer Financial Protection Bureau (“CFPB”). Foreclosure procedures and timelines vary depending on whether the property is located in a judicial or non-judicial state. Judicial states (i.e., Puerto Rico, Florida and the USVI) require the foreclosure to be processed through the state’s court while foreclosure in non-judicial states (i.e., the BVI) is processed without court intervention. Foreclosure timelines vary according to local jurisdiction law and investor guidelines. Occasionally, foreclosures may be delayed due to, among other reasons, mandatory mediations, bankruptcy, court delays and title issues
Loans Foreclosure Delinquency Threshold		120 days
Financing Receivable, Purchase		$ 800	13,400
Residential Portfolio Segment [Member] | TDR [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans in trial		2,500
Residential Portfolio Segment [Member] | Payment Deferral [Member] | COVID-19
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		511,900
Financing Receivable Deferral Payment Number Of Agreements | numberofcontracts	3,227
Residential Portfolio Segment [Member] | Government [Member] | PRHFA [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		100,800		106,900
Residential Portfolio Segment [Member] | PCD loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Residential mortgage loans in process of foreclosure		18,900
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		204,487		247,117
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | TDR [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring		312,238		316,649
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | United States [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		14,762		15,484
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Residential mortgage loans in process of foreclosure		60,400
Financing Receivable, Sale		156,800	173,400
Financing Receivable, Past Due		114,580		83,208
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | TDR [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring		58,800		60,100
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | United States [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		250		129
Residential Portfolio Segment [Member] | FNMA and FHLC loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Purchase		42	64
Residential Portfolio Segment [Member] | FNMA and FHLC loans [Member] | Performing Financing Receivable [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Sale		162,600	93,800
Residential Portfolio Segment [Member] | GNMA [Member] | Repurchase Option Program [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Purchase		55,000	22,500
Financing Receivable, Past Due		17,700		35,600
Commercial Portfolio Segment [Member] | Payment Deferral [Member] | COVID-19
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		540,800,000
Financing Receivable Deferral Payment Number Of Agreements | numberofcontracts	196
Commercial Portfolio Segment [Member] | Puerto Rico [Member] | Government [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		203,300		57,700
Commercial Portfolio Segment [Member] | Puerto Rico [Member] | Government [Member] | Municipalities [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		107,700
Commercial Portfolio Segment [Member] | Puerto Rico [Member] | Government [Member] | PREPA [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		13,800
Commercial Portfolio Segment [Member] | USVI [Member] | Government [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		64,000		64,100
Commercial Portfolio Segment [Member] | USVI [Member] | Government [Member] | Public Corporations [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		40,800
Commercial Portfolio Segment [Member] | USVI [Member] | Government [Member] | Independent Instrumentality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		23,200
Commercial Portfolio Segment [Member] | Nonperforming Financing Receivable [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for sale sold			4,800
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		19,799		9,887
Commercial Portfolio Segment [Member] | Construction Loans [Member] | TDR [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring		3,494		4,321
Commercial Portfolio Segment [Member] | Construction Loans [Member] | United States [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		4,320		0
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		41,927		45,849
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | TDR [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring		67,600		74,979
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | United States [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		1,549		870
Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		36,364		27,724
Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member] | TDR [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring		83,517		66,849
Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member] | United States [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Past Due		3,172		$ 646
Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member] | Performing Financing Receivable [Member] | Puerto Rico [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Sale			$ 48,200
Consumer Portfolio Segment [Member] | TDR [Member]
Loans and Leases Receivable Disclosure [Line Items]
Financing Receivable, Troubled Debt Restructuring		21,800
Consumer Portfolio Segment [Member] | Payment Deferral [Member] | COVID-19
Loans and Leases Receivable Disclosure [Line Items]
Loans and Leases Receivable, Gross		$ 168,700
Financing Receivable Deferral Payment Number Of Agreements | numberofcontracts	21,750