INVESTMENT SECURITIES - Available-For-Sale Investments' Fair Value And Gross Unrealized Losses (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	$ 64,559	$ 456,477
Unrealized Losses Less than 12 months	331	3,123
Fair Value 12 months or more	1,328,036	823,506
Unrealized Losses 12 months or more	39,591	21,048
Total Fair Value	1,392,595	1,279,983
Total Unrealized Losses	39,922	24,171
Equity securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months		0
Unrealized Losses Less than 12 months		0
Fair Value 12 months or more		407
Unrealized Losses 12 months or more		6
Total Fair Value		407
Total Unrealized Losses		6
Puerto Rico-government obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	0	0
Unrealized Losses Less than 12 months	0	0
Fair Value 12 months or more	2,824	2,695
Unrealized Losses 12 months or more	1,361	1,277
Total Fair Value	2,824	2,695
Total Unrealized Losses	1,361	1,277
U.S. Treasury and U.S. government agencies obligations
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	16,669	136,459
Unrealized Losses Less than 12 months	77	494
Fair Value 12 months or more	468,094	362,050
Unrealized Losses 12 months or more	6,004	4,085
Total Fair Value	484,763	498,509
Total Unrealized Losses	6,081	4,579
MBS [Member] | FNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	25,079	189,699
Unrealized Losses Less than 12 months	129	1,705
Fair Value 12 months or more	521,871	274,963
Unrealized Losses 12 months or more	17,048	5,623
Total Fair Value	546,950	464,662
Total Unrealized Losses	17,177	7,328
MBS [Member] | FHLMC [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	3,382	91,174
Unrealized Losses Less than 12 months	32	590
Fair Value 12 months or more	263,798	166,331
Unrealized Losses 12 months or more	8,517	4,326
Total Fair Value	267,180	257,505
Total Unrealized Losses	8,549	4,916
MBS [Member] | GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	3,364	39,145
Unrealized Losses Less than 12 months	15	334
Fair Value 12 months or more	57,535	0
Unrealized Losses 12 months or more	1,235	0
Total Fair Value	60,899	39,145
Total Unrealized Losses	1,250	334
MBS [Member] | Collateralized mortgage obligations issued or guaranteed by FHLMC and GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	16,065
Unrealized Losses Less than 12 months	78
Fair Value 12 months or more	0
Unrealized Losses 12 months or more	0
Total Fair Value	16,065
Total Unrealized Losses	78
MBS [Member] | Other mortgage pass-through trust certificates [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	0	0
Unrealized Losses Less than 12 months	0	0
Fair Value 12 months or more	13,914	17,060
Unrealized Losses 12 months or more	5,426	5,731
Total Fair Value	13,914	17,060
Total Unrealized Losses	$ 5,426	$ 5,731