INVESTMENT SECURITIES - Available-For-Sale Investments' Fair Value And Gross Unrealized Losses (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less than 12 months	$ 688,560	$ 278,893
Unrealized Losses Less than 12 months	2,245	1,634
Fair Value 12 months or more	42,754	358,629
Unrealized Losses 12 months or more	4,696	8,422
Total Fair Value	731,314	637,522
Total Unrealized Losses	6,941	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	2,907	2,974
Unrealized Losses 12 months or more	828	1,192
Total Fair Value	2,907	2,974
Total Unrealized Losses	828	1,192
U.S. Treasury and U.S. government agencies obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less than 12 months	242,648	45,073
Unrealized Losses Less than 12 months	1,131	172
Fair Value 12 months or more	20,985	99,764
Unrealized Losses 12 months or more	152	252
Total Fair Value	263,633	144,837
Total Unrealized Losses	1,283	424
Mortgage Backed Securities [Member] | FNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less than 12 months	147,286	58,668
Unrealized Losses Less than 12 months	399	499
Fair Value 12 months or more	0	173,708
Unrealized Losses 12 months or more	0	1,353
Total Fair Value	147,286	232,376
Total Unrealized Losses	399	1,852
Mortgage Backed Securities [Member] | FHLMC [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less than 12 months	96,439	74,134
Unrealized Losses Less than 12 months	139	270
Fair Value 12 months or more	0	63,864
Unrealized Losses 12 months or more	0	716
Total Fair Value	96,439	137,998
Total Unrealized Losses	139	986
Mortgage Backed Securities [Member] | GNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less than 12 months	122,052	79,145
Unrealized Losses Less than 12 months	437	472
Fair Value 12 months or more	0	7,203
Unrealized Losses 12 months or more	0	28
Total Fair Value	122,052	86,348
Total Unrealized Losses	437	500
Mortgage Backed Securities [Member] | Collateralized mortgage obligations issued or guaranteed by the FHLMC, FNMA and GNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value Less than 12 months	80,135	21,873
Unrealized Losses Less than 12 months	139	221
Fair Value 12 months or more	10,023	0
Unrealized Losses 12 months or more	86	0
Total Fair Value	90,158	21,873
Total Unrealized Losses	225	221
Mortgage Backed Securities [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	8,839	11,116
Unrealized Losses 12 months or more	3,630	4,881
Total Fair Value	8,839	11,116
Total Unrealized Losses	$ 3,630	$ 4,881