DEPOSITS - Narratives (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deposits [Line Items]
weighted average interest rate on total interest-bearing deposits	0.97%	0.86%
Overdrafts in demand deposits that were reclassified as loans	$ 1,700,000	$ 1,000,000
Overdrafts Prearranged Lines Of Credit	15,200,000	32,900,000
CDs in denominations of $100,000 or higher	2,800,000,000	3,000,000,000
Brokered certificates of deposit	1,150,485,000	1,439,697,000
Unamortized broker placement fees	2,200,000	2,600,000
Deposits	9,022,631,000	8,831,205,000
Amortization Of Broker Placement Fees	1,900,000	2,881,000	$ 4,563,000
Certificate Of Deposits Denominations	100,000
Accretion Of Premium From Acquisitions	100,000	200,000	$ 600,000
Amortized Cost [Member]
Deposits [Line Items]
Deposit Liabilities Collateral Issued Financial Instruments	562,500,000	583,900,000
Market Value [Member]
Deposits [Line Items]
Deposit Liabilities Collateral Issued Financial Instruments	$ 542,900,000	$ 521,300,000
Brokered Certificate of Deposits [Member]
Deposits [Line Items]
Weighted Average Interest Rate of Time Deposits, $100,000 or More	1.50%	1.18%
Government [Member]
Deposits [Line Items]
Deposits	$ 652,000,000	$ 563,700,000
Government [Member] | Puerto Rico [Member]
Deposits [Line Items]
Deposits	490,300,000	408,800,000
Government [Member] | Virgin Islands [Member]
Deposits [Line Items]
Deposits	$ 161,700,000	$ 154,900,000