DEBT SECURITIES - Investment Securities Available for Sale (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]
Amortized cost	$ 6,021,072		$ 6,398,197
Gross Unrealized Gains	73		247
Gross Unrealized Losses	844,877		798,466
Allowance for Credit Losses	465	$ 433	458	$ 664	$ 676	$ 1,105
Fair value	$ 5,175,803		$ 5,599,520
Weighted-average yield	1.24%		1.22%
Interest receivable	$ 68,783		$ 69,730
Available-for-sale Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Interest receivable	10,800		11,100
Federal Home Loan Bank Borrowings [Member] | Asset Pledged as Collateral [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	587,000		286,500
Fair value	521,300		250,600
Fair value, net of haircut	495,300		238,100
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year	47,585		7,493
Gross Unrealized Gains Due within one year	0		0
Gross Unrealized Losses Due within one year	1,313		309
Allowance for Credit Losses within one year	0		0
Fair value Due within one year	$ 46,272		$ 7,184
Weighted-average yield Due within one year	0.54%		0.22%
Amortized cost After 1 to 5 years	$ 100,671		$ 141,366
Gross Unrealized Gains After 1 to 5 years	0		0
Gross Unrealized Losses After 1 to 5 years	6,220		9,675
Allowance for Credit Losses After 1 to 5 years	0		0
Fair value After 1 to 5 years	$ 94,451		$ 131,691
Weighted-average yield After 1 to 5 years	0.74%		0.70%
U.S. GSE's obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year	$ 271,134		$ 129,018
Gross Unrealized Gains Due within one year	0		0
Gross Unrealized Losses Due within one year	7,334		4,036
Allowance for Credit Losses within one year	0		0
Fair value Due within one year	$ 263,800		$ 124,982
Weighted-average yield Due within one year	0.73%		0.32%
Amortized cost After 1 to 5 years	$ 2,225,242		$ 2,395,273
Gross Unrealized Gains After 1 to 5 years	55		22
Gross Unrealized Losses After 1 to 5 years	201,084		227,724
Allowance for Credit Losses After 1 to 5 years	0		0
Fair value After 1 to 5 years	$ 2,024,213		$ 2,167,571
Weighted-average yield After 1 to 5 years	0.84%		0.83%
Amortized cost After 5 to 10 years	$ 10,097		$ 56,251
Gross Unrealized Gains After 5 to 10 years	0		13
Gross Unrealized Losses After 5 to 10 years	1,158		7,670
Allowance for Credit Losses After 5 to 10 years	0		0
Fair value After 5 to 10 years	$ 8,939		$ 48,594
Weighted-average yield After 5 to 10 years	2.95%		1.54%
Amortized cost After 10 years	$ 10,621		$ 12,170
Gross Unrealized Gains After 10 years	18		36
Gross Unrealized Losses After 10 years	1		0
Allowance for Credit Losses After 10 years	0		0
Fair value After 10 years	$ 10,638		$ 12,206
Weighted-average yield After 10 years	5.65%		4.62%
Puerto Rico government obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 10 years	$ 3,204		$ 3,331
Gross Unrealized Gains After 10 years	0		0
Gross Unrealized Losses After 10 years	1,374		755
Allowance for Credit Losses After 10 years	382		375
Fair value After 10 years	$ 1,448		$ 2,201
Weighted-average yield After 10 years	0.00%		0.00%
Allowance for Credit Losses	$ 382	$ 350	$ 375	$ 374	$ 386	$ 308
United States And Puerto Rico Government Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	2,668,554		2,744,902
Gross Unrealized Gains	73		71
Gross Unrealized Losses	218,484		250,169
Allowance for Credit Losses	382		375
Fair value	$ 2,449,761		$ 2,494,429
Weighted-average yield	0.84%		0.83%
Residential MBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 3,159,362		$ 3,455,864
Gross Unrealized Gains	0		176
Gross Unrealized Losses	578,884		514,499
Allowance for Credit Losses	83		83
Fair value	$ 2,580,395		$ 2,941,458
Weighted-average yield	1.54%		1.52%
Residential MBS [Member] | FHLMC [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 21,356		$ 4,235
Gross Unrealized Gains After 1 to 5 years	0		0
Gross Unrealized Losses After 1 to 5 years	1,205		169
Allowance for Credit Losses After 1 to 5 years	0		0
Fair value After 1 to 5 years	$ 20,151		$ 4,066
Weighted-average yield After 1 to 5 years	2.06%		2.33%
Amortized cost After 5 to 10 years	$ 160,407		$ 201,072
Gross Unrealized Gains After 5 to 10 years	0		0
Gross Unrealized Losses After 5 to 10 years	18,393		18,709
Allowance for Credit Losses After 5 to 10 years	0		0
Fair value After 5 to 10 years	$ 142,014		$ 182,363
Weighted-average yield After 5 to 10 years	1.55%		1.55%
Amortized cost After 10 years	$ 1,013,862		$ 1,092,289
Gross Unrealized Gains After 10 years	0		0
Gross Unrealized Losses After 10 years	211,720		186,558
Allowance for Credit Losses After 10 years	0		0
Fair value After 10 years	$ 802,142		$ 905,731
Weighted-average yield After 10 years	1.40%		1.38%
Amortized cost	$ 1,195,625		$ 1,297,596
Gross Unrealized Gains	0		0
Gross Unrealized Losses	231,318		205,436
Allowance for Credit Losses	0		0
Fair value	$ 964,307		$ 1,092,160
Weighted-average yield	1.43%		1.41%
Residential MBS [Member] | GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year			$ 5
Gross Unrealized Gains Due within one year			0
Gross Unrealized Losses Due within one year			0
Allowance for Credit Losses within one year			0
Fair value Due within one year			$ 5
Weighted-average yield Due within one year			1.73%
Amortized cost After 1 to 5 years	$ 19,559		$ 15,508
Gross Unrealized Gains After 1 to 5 years	0		0
Gross Unrealized Losses After 1 to 5 years	1,207		622
Allowance for Credit Losses After 1 to 5 years	0		0
Fair value After 1 to 5 years	$ 18,352		$ 14,886
Weighted-average yield After 1 to 5 years	1.27%		2.00%
Amortized cost After 5 to 10 years	$ 28,587		$ 45,322
Gross Unrealized Gains After 5 to 10 years	0		1
Gross Unrealized Losses After 5 to 10 years	3,127		3,809
Allowance for Credit Losses After 5 to 10 years	0		0
Fair value After 5 to 10 years	$ 25,460		$ 41,514
Weighted-average yield After 5 to 10 years	1.59%		1.31%
Amortized cost After 10 years	$ 212,835		$ 232,632
Gross Unrealized Gains After 10 years	0		51
Gross Unrealized Losses After 10 years	33,476		27,169
Allowance for Credit Losses After 10 years	0		0
Fair value After 10 years	$ 179,359		$ 205,514
Weighted-average yield After 10 years	2.58%		2.47%
Amortized cost	$ 260,981		$ 293,467
Gross Unrealized Gains	0		52
Gross Unrealized Losses	37,810		31,600
Allowance for Credit Losses	0		0
Fair value	$ 223,171		$ 261,919
Weighted-average yield	2.38%		2.27%
Residential MBS [Member] | FNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 35,343		$ 9,685
Gross Unrealized Gains After 1 to 5 years	0		0
Gross Unrealized Losses After 1 to 5 years	1,992		521
Allowance for Credit Losses After 1 to 5 years	0		0
Fair value After 1 to 5 years	$ 33,351		$ 9,164
Weighted-average yield After 1 to 5 years	2.11%		1.76%
Amortized cost After 5 to 10 years	$ 307,379		$ 358,346
Gross Unrealized Gains After 5 to 10 years	0		0
Gross Unrealized Losses After 5 to 10 years	35,138		31,620
Allowance for Credit Losses After 5 to 10 years	0		0
Fair value After 5 to 10 years	$ 272,241		$ 326,726
Weighted-average yield After 5 to 10 years	1.70%		1.68%
Amortized cost After 10 years	$ 1,072,667		$ 1,186,635
Gross Unrealized Gains After 10 years	0		124
Gross Unrealized Losses After 10 years	207,428		186,757
Allowance for Credit Losses After 10 years	0		0
Fair value After 10 years	$ 865,239		$ 1,000,002
Weighted-average yield After 10 years	1.36%		1.38%
Amortized cost	$ 1,415,389		$ 1,554,666
Gross Unrealized Gains	0		124
Gross Unrealized Losses	244,558		218,898
Allowance for Credit Losses	0		0
Fair value	$ 1,170,831		$ 1,335,892
Weighted-average yield	1.45%		1.45%
Residential MBS [Member] | Collateralized mortgage obligations ("CMOs") issued or guaranteed by FHLMC, FNMA and GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 10 years	$ 280,056		$ 302,232
Gross Unrealized Gains After 10 years	0		0
Gross Unrealized Losses After 10 years	62,888		56,539
Allowance for Credit Losses After 10 years	0		0
Fair value After 10 years	$ 217,168		$ 245,693
Weighted-average yield After 10 years	1.54%		1.44%
Residential MBS [Member] | Private label [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 10 years	$ 7,311		$ 7,903
Gross Unrealized Gains After 10 years	0		0
Gross Unrealized Losses After 10 years	2,310		2,026
Allowance for Credit Losses After 10 years	83		83
Fair value After 10 years	$ 4,918		$ 5,794
Weighted-average yield After 10 years	7.73%		6.83%
Allowance for Credit Losses	$ 100		$ 100
Weighted-average yield	7.73%
Commercial Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 44,111		30,578
Gross Unrealized Gains After 1 to 5 years	0		0
Gross Unrealized Losses After 1 to 5 years	8,631		4,463
Allowance for Credit Losses After 1 to 5 years	0		0
Fair value After 1 to 5 years	$ 35,480		$ 26,115
Weighted-average yield After 1 to 5 years	2.18%		2.43%
Amortized cost After 5 to 10 years	$ 25,522		$ 44,889
Gross Unrealized Gains After 5 to 10 years	0		0
Gross Unrealized Losses After 5 to 10 years	4,067		5,603
Allowance for Credit Losses After 5 to 10 years	0		0
Fair value After 5 to 10 years	$ 21,455		$ 39,286
Weighted-average yield After 5 to 10 years	2.13%		1.89%
Amortized cost After 10 years	$ 123,523		$ 121,464
Gross Unrealized Gains After 10 years	0		0
Gross Unrealized Losses After 10 years	34,811		23,732
Allowance for Credit Losses After 10 years	0		0
Fair value After 10 years	$ 88,712		$ 97,732
Weighted-average yield After 10 years	1.36%		1.23%
Amortized cost	$ 193,156		$ 196,931
Gross Unrealized Gains	0		0
Gross Unrealized Losses	47,509		33,798
Allowance for Credit Losses	0		0
Fair value	$ 145,647		$ 163,133
Weighted-average yield	1.65%		1.56%
Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 3,352,518		$ 3,652,795
Gross Unrealized Gains	0		176
Gross Unrealized Losses	626,393		548,297
Allowance for Credit Losses	83		83
Fair value	$ 2,726,042		$ 3,104,591
Weighted-average yield	1.55%		1.52%
Other Debt Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year			$ 500
Gross Unrealized Gains Due within one year			0
Gross Unrealized Losses Due within one year			0
Allowance for Credit Losses within one year			0
Fair value Due within one year			$ 500
Weighted-average yield Due within one year			0.84%
Unisured Portion Of Government Deposits [Member] | Asset Pledged as Collateral [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 3,200,000		$ 2,800,000
Fair value	$ 2,800,000		$ 2,400,000