LOANS HELD FOR INVESTMENT - Corporation's Aging of Loans Held for Investment Portfolio (Parenthetical) (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Current	$ 11,378,197,000	$ 8,493,827,000
Financing Receivable, Past Due	469,078,000	508,378,000
Loans held for investment	11,847,275,000	9,002,205,000
Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Current	9,391,021,000	6,639,398,000
Financing Receivable, Past Due	443,180,000	488,879,000
Loans held for investment	9,834,201,000	7,128,277,000
Florida region [Member]
Financing Receivable, Past Due [Line Items]
Current	1,987,176,000	1,854,429,000
Financing Receivable, Past Due	25,898,000	19,499,000
Loans held for investment	2,013,074,000	1,873,928,000
30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	46,432,000	55,640,000
30-59 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	38,586,000	53,892,000
30-59 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	7,846,000	1,748,000
60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	63,946,000	107,028,000
60-89 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	62,110,000	103,691,000
60-89 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,836,000	3,337,000
90 days or more Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	358,700,000	345,710,000
90 days or more Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	342,484,000	331,296,000
90 days or more Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	16,216,000	14,414,000
PCD loans [Member]
Financing Receivable, Past Due [Line Items]
Loans held for investment	133,200,000	136,700,000
PCD loans [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Loans held for investment	133,200,000	136,700,000
Consumer Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,572,086,000	2,281,653,000
Consumer Portfolio Segment [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Loans held for investment	2,541,960,000	2,241,131,000
Consumer Portfolio Segment [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Loans held for investment	$ 30,126,000	$ 40,522,000
Consumer Portfolio Segment [Member] | Credit Card [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Threshold Period Past Due, Writeoff	180 days	180 days
Consumer Portfolio Segment [Member] | Credit Card [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Threshold Period Past Due, Writeoff	180 days	180 days
Residential Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans held for investment	$ 3,636,713,000	$ 2,933,773,000
Residential Portfolio Segment [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Loans held for investment	3,100,359,000	2,367,587,000
Residential Portfolio Segment [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Loans held for investment	536,354,000	566,186,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member]
Financing Receivable, Past Due [Line Items]
Current	3,269,424,000	2,562,747,000
Financing Receivable, Past Due	204,487,000	247,117,000
Loans held for investment	3,473,911,000	2,809,864,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Current	2,749,008,000	2,013,525,000
Financing Receivable, Past Due	189,725,000	231,633,000
Loans held for investment	2,938,733,000	2,245,158,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Current	520,416,000	549,222,000
Financing Receivable, Past Due	14,762,000	15,484,000
Loans held for investment	535,178,000	564,706,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Loans held for investment	111,000,000.0	116,200,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | 30-59 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Loans held for investment	96,600,000	110,500,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | 30-59 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Loans held for investment	14,400,000	5,800,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	41,095,000	85,501,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | 60-89 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	40,833,000	83,308,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | 60-89 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	262,000	2,193,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | 90 days or more Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	163,392,000	161,616,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | 90 days or more Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	148,892,000	148,325,000
Residential Portfolio Segment [Member] | Conventional residential mortgage loans [Member] | 90 days or more Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	14,500,000	13,291,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, 15 Months or More Past Due, No Still Accruing	$ 54,100,000	$ 37,900,000
Period Of Residential Mortgage Loan That Are No Longer Accruing Interest	15 months	15 months
Current	$ 48,222,000	$ 40,701,000
Financing Receivable, Past Due	114,580,000	83,208,000
Loans held for investment	162,802,000	123,909,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, 15 Months or More Past Due, No Still Accruing	$ 54,100,000	$ 37,900,000
Period Of Residential Mortgage Loan That Are No Longer Accruing Interest	15 months	15 months
Current	$ 47,296,000	$ 39,350,000
Financing Receivable, Past Due	114,330,000	83,079,000
Loans held for investment	161,626,000	122,429,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, 15 Months or More Past Due, No Still Accruing	$ 0	$ 0
Period Of Residential Mortgage Loan That Are No Longer Accruing Interest	15 months	15 months
Current	$ 926,000	$ 1,351,000
Financing Receivable, Past Due	250,000	129,000
Loans held for investment	1,176,000	1,480,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Loans held for investment	6,300,000	7,100,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | 30-59 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Loans held for investment	6,100,000	6,700,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | 30-59 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Loans held for investment		400,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	3,448,000	2,068,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | 60-89 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	3,448,000	2,068,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | 60-89 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | 90 days or more Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	111,132,000	81,140,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | 90 days or more Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	110,882,000	81,011,000
Residential Portfolio Segment [Member] | FHA/VA government-guaranteed loans [Member] | 90 days or more Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	250,000	129,000
Residential Portfolio Segment [Member] | GNMA [Member] | Repurchase Option Program [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	17,700,000	35,600,000
Residential Portfolio Segment [Member] | GNMA [Member] | Repurchase Option Program [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	17,700,000	35,600,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member]
Financing Receivable, Past Due [Line Items]
Current	2,178,350,000	1,398,737,000
Financing Receivable, Past Due	41,927,000	45,849,000
Loans held for investment	2,220,277,000	1,444,586,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Current	1,793,903,000	1,034,921,000
Financing Receivable, Past Due	40,378,000	44,979,000
Loans held for investment	1,834,281,000	1,079,900,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Current	384,447,000	363,816,000
Financing Receivable, Past Due	1,549,000	870,000
Loans held for investment	385,996,000	364,686,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	2,168,000	0
Loans held for investment	8,300,000	6,600,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | 30-59 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	973,000	0
Loans held for investment	6,700,000	6,000,000.0
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | 30-59 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,195,000	0
Loans held for investment		600,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	6,780,000	3,551,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | 60-89 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	6,426,000	2,681,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | 60-89 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	354,000	870,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | 90 days or more Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	32,979,000	42,298,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | 90 days or more Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	32,979,000	42,298,000
Commercial Portfolio Segment [Member] | Mortgage Receivable [Member] | 90 days or more Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Commercial Portfolio Segment [Member] | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Current	171,557,000	101,430,000
Financing Receivable, Past Due	19,799,000	9,887,000
Loans held for investment	191,356,000	111,317,000
Commercial Portfolio Segment [Member] | Construction Loans [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Current	54,527,000	38,359,000
Financing Receivable, Past Due	15,479,000	9,887,000
Loans held for investment	70,006,000	48,246,000
Commercial Portfolio Segment [Member] | Construction Loans [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Current	117,030,000	63,071,000
Financing Receivable, Past Due	4,320,000	0
Loans held for investment	121,350,000	63,071,000
Commercial Portfolio Segment [Member] | Construction Loans [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	4,912,000	0
Loans held for investment	500,000	100,000
Commercial Portfolio Segment [Member] | Construction Loans [Member] | 30-59 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	592,000	0
Loans held for investment	500,000	100,000
Commercial Portfolio Segment [Member] | Construction Loans [Member] | 30-59 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	4,320,000	0
Commercial Portfolio Segment [Member] | Construction Loans [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,797,000	105,000
Commercial Portfolio Segment [Member] | Construction Loans [Member] | 60-89 Days Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	1,797,000	105,000
Commercial Portfolio Segment [Member] | Construction Loans [Member] | 60-89 Days Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	0	0
Commercial Portfolio Segment [Member] | Construction Loans [Member] | 90 days or more Past Due [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	13,090,000	9,782,000
Commercial Portfolio Segment [Member] | Construction Loans [Member] | 90 days or more Past Due [Member] | Puerto Rico and Virgin Islands regions [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	13,090,000	9,782,000
Commercial Portfolio Segment [Member] | Construction Loans [Member] | 90 days or more Past Due [Member] | Florida region [Member]
Financing Receivable, Past Due [Line Items]
Financing Receivable, Past Due	$ 0	$ 0