DEBT SECURITIES - Available-For-Sale Investments' Fair Value And Gross Unrealized Losses (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	$ 46,731		$ 1,115,192
Unrealized Losses Less than 12 months	1,619		125,343
Fair Value 12 months or more	5,114,046		4,447,686
Unrealized Losses 12 months or more	843,258		673,123
Total Fair Value	5,160,777		5,562,878
Total Unrealized Losses	844,877		798,466
Allowance for Credit Losses	465	$ 433	458	$ 664	$ 676	$ 1,105
U.S. Treasury and U.S. government agencies obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	3,204		298,313
Unrealized Losses Less than 12 months	5		18,057
Fair Value 12 months or more	2,430,083		2,174,724
Unrealized Losses 12 months or more	217,105		231,357
Total Fair Value	2,433,287		2,473,037
Total Unrealized Losses	217,110		249,414
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	1,448		2,201
Unrealized Losses 12 months or more	1,374		755
Total Fair Value	1,448		2,201
Total Unrealized Losses	1,374		755
Allowance for Credit Losses	382	350	375	374	386	308
Residential MBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Allowance for Credit Losses	83		83
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	12		260,524
Unrealized Losses Less than 12 months	1		45,424
Fair Value 12 months or more	964,295		831,637
Unrealized Losses 12 months or more	231,317		160,012
Total Fair Value	964,307		1,092,161
Total Unrealized Losses	231,318		205,436
Residential MBS [Member] | GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	22,811		74,829
Unrealized Losses Less than 12 months	1,220		3,433
Fair Value 12 months or more	200,360		179,854
Unrealized Losses 12 months or more	36,590		28,167
Total Fair Value	223,171		254,683
Total Unrealized Losses	37,810		31,600
Residential MBS [Member] | FNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	9,195		405,977
Unrealized Losses Less than 12 months	191		49,479
Fair Value 12 months or more	1,161,636		920,200
Unrealized Losses 12 months or more	244,367		169,419
Total Fair Value	1,170,831		1,326,177
Total Unrealized Losses	244,558		218,898
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		45,370
Unrealized Losses Less than 12 months	0		6,735
Fair Value 12 months or more	217,168		200,323
Unrealized Losses 12 months or more	62,888		49,804
Total Fair Value	217,168		245,693
Total Unrealized Losses	62,888		56,539
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	4,918		5,794
Unrealized Losses 12 months or more	2,310		2,026
Total Fair Value	4,918		5,794
Total Unrealized Losses	2,310		2,026
Allowance for Credit Losses	83	$ 83	83	$ 290	$ 290	$ 797
Commercial MBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	11,509		30,179
Unrealized Losses Less than 12 months	202		2,215
Fair Value 12 months or more	134,138		132,953
Unrealized Losses 12 months or more	47,307		31,583
Total Fair Value	145,647		163,132
Total Unrealized Losses	47,509		33,798
Allowance for Credit Losses	$ 0		$ 0