DEBT SECURITIES - Available-For-Sale Investments' Fair Value And Gross Unrealized Losses (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	$ 17,006	$ 26,180
Unrealized Losses Less than 12 months	101	120
Fair Value 12 months or more	4,990,759	5,170,265
Unrealized Losses 12 months or more	648,036	632,929
Total Fair Value	5,007,765	5,196,445
Total Unrealized Losses	648,137	633,049
Allowance for Credit Losses	442	511	$ 449	$ 458
U.S. Treasury and U.S. government agencies obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	4,238	2,544
Unrealized Losses Less than 12 months	5	2
Fair Value 12 months or more	2,354,777	2,428,784
Unrealized Losses 12 months or more	151,053	157,026
Total Fair Value	2,359,015	2,431,328
Total Unrealized Losses	151,058	157,028
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	1,551	1,415
Unrealized Losses 12 months or more	1,235	1,346
Total Fair Value	1,551	1,415
Total Unrealized Losses	1,235	1,346
Allowance for Credit Losses	326	395	366	375
Residential MBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Allowance for Credit Losses	116	116
Residential MBS [Member] | Private label [Member]
Schedule Of Available For Sale Securities [Line Items]
Allowance for Credit Losses	100	100
Residential MBS [Member] | FHLMC [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	7	9
Unrealized Losses Less than 12 months	0	0
Fair Value 12 months or more	950,687	988,092
Unrealized Losses 12 months or more	183,413	174,786
Total Fair Value	950,694	988,101
Total Unrealized Losses	183,413	174,786
Residential MBS [Member] | GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	3,452	12,257
Unrealized Losses Less than 12 months	20	100
Fair Value 12 months or more	195,424	202,390
Unrealized Losses 12 months or more	28,907	25,808
Total Fair Value	198,876	214,647
Total Unrealized Losses	28,927	25,908
Residential MBS [Member] | FNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	3,963	0
Unrealized Losses Less than 12 months	11	0
Fair Value 12 months or more	1,134,624	1,183,275
Unrealized Losses 12 months or more	187,689	180,913
Total Fair Value	1,138,587	1,183,275
Total Unrealized Losses	187,700	180,913
Residential MBS [Member] | CMOs issued or guaranteed by the FHLMC, FNMA, and GNMA: [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	211,178	221,276
Unrealized Losses 12 months or more	53,977	52,263
Total Fair Value	211,178	221,276
Total Unrealized Losses	53,977	52,263
Residential MBS [Member] | Private label [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	4,724	4,785
Unrealized Losses 12 months or more	2,056	2,185
Total Fair Value	4,724	4,785
Total Unrealized Losses	2,056	2,185
Allowance for Credit Losses	116	116	$ 83	$ 83
Commercial MBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	5,346	11,370
Unrealized Losses Less than 12 months	65	18
Fair Value 12 months or more	137,794	140,248
Unrealized Losses 12 months or more	39,706	38,602
Total Fair Value	143,140	151,618
Total Unrealized Losses	39,771	38,620
Allowance for Credit Losses	$ 0	$ 0