INVESTMENT SECURITIES - Available-For-Sale Investments' Fair Value And Gross Unrealized Losses (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	$ 782,960	$ 278,893
Unrealized Losses Less than 12 months	1,610	1,634
Fair Value 12 months or more	44,465	358,629
Unrealized Losses 12 months or more	3,907	8,422
Total Fair Value	827,425	637,522
Total Unrealized Losses	5,517	10,056
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	2,899	2,974
Unrealized Losses 12 months or more	780	1,192
Total Fair Value	2,899	2,974
Total Unrealized Losses	780	1,192
U.S. Treasury and U.S. government agencies obligations
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	425,155	45,073
Unrealized Losses Less than 12 months	621	172
Fair Value 12 months or more	23,377	99,764
Unrealized Losses 12 months or more	165	252
Total Fair Value	448,532	144,837
Total Unrealized Losses	786	424
MBS [Member] | FNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	93,509	58,668
Unrealized Losses Less than 12 months	203	499
Fair Value 12 months or more	0	173,708
Unrealized Losses 12 months or more	0	1,353
Total Fair Value	93,509	232,376
Total Unrealized Losses	203	1,852
MBS [Member] | FHLMC [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	89,292	74,134
Unrealized Losses Less than 12 months	159	270
Fair Value 12 months or more	0	63,864
Unrealized Losses 12 months or more	0	716
Total Fair Value	89,292	137,998
Total Unrealized Losses	159	986
MBS [Member] | GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	70,504	79,145
Unrealized Losses Less than 12 months	217	472
Fair Value 12 months or more	0	7,203
Unrealized Losses 12 months or more	0	28
Total Fair Value	70,504	86,348
Total Unrealized Losses	217	500
MBS [Member] | Collateralized mortgage obligations guaranteed by FHLMC, FNMA and GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	104,500	21,873
Unrealized Losses Less than 12 months	410	221
Fair Value 12 months or more	9,761	0
Unrealized Losses 12 months or more	82	0
Total Fair Value	114,261	21,873
Total Unrealized Losses	492	221
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	8,428	11,116
Unrealized Losses 12 months or more	2,880	4,881
Total Fair Value	8,428	11,116
Total Unrealized Losses	$ 2,880	$ 4,881