LOANS HELD FOR INVESTMENT - Breakdown Between Accrual and Nonaccrual Status of TDRs (Detail) - Entity Loan Modification Program [Member] - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	$ 375,740		$ 393,327
Financing Receivable Modifications Recorded Investment Nonaccrual Status	52,860		85,869
Financing Receivable, Troubled Debt Restructuring	428,600	$ 450,078	479,196	$ 488,615	$ 496,207	$ 487,997
Residential Portfolio Segment [Member] | Conventional Loan [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	243,685		256,779
Financing Receivable Modifications Recorded Investment Nonaccrual Status	20,648		53,827
Financing Receivable, Troubled Debt Restructuring	264,333		310,606
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	2,315		2,480
Financing Receivable Modifications Recorded Investment Nonaccrual Status	729		943
Financing Receivable, Troubled Debt Restructuring	3,044		3,423
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	53,335		45,627
Financing Receivable Modifications Recorded Investment Nonaccrual Status	16,228		18,811
Financing Receivable, Troubled Debt Restructuring	69,563		64,438
Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	64,354		73,649
Financing Receivable Modifications Recorded Investment Nonaccrual Status	11,933		6,833
Financing Receivable, Troubled Debt Restructuring	76,287		80,482
Consumer Portfolio Segment [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring	15,400
Consumer Portfolio Segment [Member] | Auto loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	4,711		6,551
Financing Receivable Modifications Recorded Investment Nonaccrual Status	3,024		4,968
Financing Receivable, Troubled Debt Restructuring	7,735		11,519
Consumer Portfolio Segment [Member] | Finance Leases [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	1,024		1,125
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		19
Financing Receivable, Troubled Debt Restructuring	1,024		1,144
Consumer Portfolio Segment [Member] | Personal Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	914		920
Financing Receivable Modifications Recorded Investment Nonaccrual Status	2		4
Financing Receivable, Troubled Debt Restructuring	916		924
Consumer Portfolio Segment [Member] | Other Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	2,767		3,838
Financing Receivable Modifications Recorded Investment Nonaccrual Status	296		464
Financing Receivable, Troubled Debt Restructuring	3,063		4,302
Consumer Portfolio Segment [Member] | Credit cards [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	2,635		2,358
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		0
Financing Receivable, Troubled Debt Restructuring	2,635		2,358
Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	369,910		386,720
Financing Receivable Modifications Recorded Investment Nonaccrual Status	51,062		85,297
Financing Receivable, Troubled Debt Restructuring	420,972		472,017
Puerto Rico and Virgin Islands regions [Member] | Residential Portfolio Segment [Member] | Conventional Loan [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	240,632		253,421
Financing Receivable Modifications Recorded Investment Nonaccrual Status	19,292		53,516
Financing Receivable, Troubled Debt Restructuring	259,924		306,937
Puerto Rico and Virgin Islands regions [Member] | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	2,315		2,480
Financing Receivable Modifications Recorded Investment Nonaccrual Status	729		943
Financing Receivable, Troubled Debt Restructuring	3,044		3,423
Puerto Rico and Virgin Islands regions [Member] | Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	51,055		43,012
Financing Receivable Modifications Recorded Investment Nonaccrual Status	16,228		18,811
Financing Receivable, Troubled Debt Restructuring	67,283		61,823
Puerto Rico and Virgin Islands regions [Member] | Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	64,354		73,649
Financing Receivable Modifications Recorded Investment Nonaccrual Status	11,491		6,609
Financing Receivable, Troubled Debt Restructuring	75,845		80,258
Puerto Rico and Virgin Islands regions [Member] | Consumer Portfolio Segment [Member] | Auto loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	4,671		6,481
Financing Receivable Modifications Recorded Investment Nonaccrual Status	3,024		4,968
Financing Receivable, Troubled Debt Restructuring	7,695		11,449
Puerto Rico and Virgin Islands regions [Member] | Consumer Portfolio Segment [Member] | Finance Leases [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	1,024		1,125
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		19
Financing Receivable, Troubled Debt Restructuring	1,024		1,144
Puerto Rico and Virgin Islands regions [Member] | Consumer Portfolio Segment [Member] | Personal Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	914		920
Financing Receivable Modifications Recorded Investment Nonaccrual Status	2		4
Financing Receivable, Troubled Debt Restructuring	916		924
Puerto Rico and Virgin Islands regions [Member] | Consumer Portfolio Segment [Member] | Other Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	2,310		3,274
Financing Receivable Modifications Recorded Investment Nonaccrual Status	296		427
Financing Receivable, Troubled Debt Restructuring	2,606		3,701
Puerto Rico and Virgin Islands regions [Member] | Consumer Portfolio Segment [Member] | Credit cards [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	2,635		2,358
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		0
Financing Receivable, Troubled Debt Restructuring	2,635		2,358
Florida region
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	5,830		6,607
Financing Receivable Modifications Recorded Investment Nonaccrual Status	1,798		572
Financing Receivable, Troubled Debt Restructuring	7,628		7,179
Florida region | Residential Portfolio Segment [Member] | Conventional Loan [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	3,053		3,358
Financing Receivable Modifications Recorded Investment Nonaccrual Status	1,356		311
Financing Receivable, Troubled Debt Restructuring	4,409		3,669
Florida region | Commercial Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	0		0
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		0
Financing Receivable, Troubled Debt Restructuring	0		0
Florida region | Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	2,280		2,615
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		0
Financing Receivable, Troubled Debt Restructuring	2,280		2,615
Florida region | Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	0		0
Financing Receivable Modifications Recorded Investment Nonaccrual Status	442		224
Financing Receivable, Troubled Debt Restructuring	442		224
Florida region | Consumer Portfolio Segment [Member] | Auto loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	40		70
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		0
Financing Receivable, Troubled Debt Restructuring	40		70
Florida region | Consumer Portfolio Segment [Member] | Finance Leases [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	0		0
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		0
Financing Receivable, Troubled Debt Restructuring	0		0
Florida region | Consumer Portfolio Segment [Member] | Personal Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	0		0
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		0
Financing Receivable, Troubled Debt Restructuring	0		0
Florida region | Consumer Portfolio Segment [Member] | Other Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	457		564
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		37
Financing Receivable, Troubled Debt Restructuring	457		601
Florida region | Consumer Portfolio Segment [Member] | Credit cards [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable Modifications Recorded Investment Accrual Status	0		0
Financing Receivable Modifications Recorded Investment Nonaccrual Status	0		0
Financing Receivable, Troubled Debt Restructuring	$ 0		$ 0