DEPOSITS - Narratives (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deposits [Line Items]
weighted average interest rate on total interest-bearing deposits	1.03%	0.97%
Overdrafts in demand deposits that were reclassified as loans	$ 2,100,000	$ 1,700,000
Overdrafts Prearranged Lines Of Credit	21,700,000	15,200,000
CDs in denominations of $100,000 or higher	2,200,000,000	2,800,000,000
Brokered certificates of deposit	$ 555,597,000	$ 1,150,485,000
Weighted Average Interest Rate of Time Deposits, $100,000 or More	5.66%	3.64%
Unamortized broker placement fees	$ 1,100,000	$ 2,200,000
Deposits	8,994,714,000	9,022,631,000
Market value of uninsured portions collateralized by securities and loans	592,900,000	542,900,000
Amortized cost of uninsured portions collateralized by securities and loans	615,700,000	562,500,000
Certificate Of Deposits Denominations	100,000
Accretion Of Premium From Acquisition	9,000	100,000	$ 200,000
Letters of credit issued by the FHLB as pledges for public deposits in the Virgin Islands	1,900,000,000	1,900,000,000
Amortization Of Broker Placement Fees	$ 1,163,000	$ 1,900,000	2,881,000
CDs including brokered CDs [Member]
Deposits [Line Items]
Weighted Average Interest Rate of Time Deposits, $100,000 or More	1.88%	1.50%
Federal Home Loan Bank [Member]
Deposits [Line Items]
Letters of credit issued by the FHLB as pledges for public deposits in the Virgin Islands	$ 1,700,000,000	$ 1,700,000,000
Government [Member]
Deposits [Line Items]
Deposits	900,800,000	652,000,000
Puerto Rico [Member]
Deposits [Line Items]
Brokered certificates of deposit	441,100,000	1,000,000,000	1,400,000,000
Deposits	6,208,531,000	6,268,056,000	6,291,353,000
Puerto Rico [Member] | Government [Member]
Deposits [Line Items]
Deposits	677,300,000	490,300,000
United States [Member]
Deposits [Line Items]
Brokered certificates of deposit	114,500,000	158,000,000	60,100,000
Deposits	1,519,362,000	1,637,941,000	1,564,839,000
Virgin Islands [Member]
Deposits [Line Items]
Deposits	1,266,821,000	1,116,634,000	$ 975,013,000
Virgin Islands [Member] | Federal Home Loan Bank [Member]
Deposits [Line Items]
Letters of credit issued by the FHLB as pledges for public deposits in the Virgin Islands	182,000,000
Virgin Islands [Member] | Government [Member]
Deposits [Line Items]
Deposits	$ 223,400,000	$ 161,700,000