INVESTMENT SECURITIES - Investment Securities Available for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 4,584,851	$ 2,109,008
Gross unrealized gain	68,995	24,573
Gross unrealized loss	5,517	10,056
Allowance for Credit Losses	1,310	0
Fair value	$ 4,647,019	$ 2,123,525
Weighted-average yield	1.28%	2.52%
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year	$ 7,498
Gross Unrealized gains Due within one year	9
Gross Unrealized losses Due within one year	0
Allowance for Credit Losses within one year	0
Fair value Due within one year	$ 7,507
Weighted-average yield Due within one year	1.65%
Amortized cost After 1 to 5 years		$ 7,478
Gross Unrealized gains After 1 to 5 years		1
Gross Unrealized losses After 1 to 5 years		0
Fair value After 1 to 5 years		$ 7,479
Weighted-average yield After 1 to 5 years		1.65%
U.S. government-sponsored agencies obigations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year	$ 24,413	$ 93,299
Gross Unrealized gains Due within one year	273	103
Gross Unrealized losses Due within one year	0	106
Allowance for Credit Losses within one year	0
Fair value Due within one year	$ 24,686	$ 93,296
Weighted-average yield Due within one year	1.95%	1.67%
Amortized cost After 1 to 5 years	$ 691,668	$ 142,513
Gross Unrealized gains After 1 to 5 years	911	676
Gross Unrealized losses After 1 to 5 years	290	52
Allowance for Credit Losses After 1 to 5 years	0
Fair value After 1 to 5 years	$ 692,289	$ 143,137
Weighted-average yield After 1 to 5 years	0.57%	2.12%
Amortized cost After 5 to 10 years	$ 441,454	$ 63,764
Gross Unrealized gains After 5 to 10 years	821	165
Gross Unrealized losses After 5 to 10 years	347	150
Allowance for Credit Losses After 5 to 10 years	0
Fair value After 5 to 10 years	$ 441,928	$ 63,779
Weighted-average yield After 5 to 10 years	0.83%	2.33%
Amortized cost After 10 years	$ 21,413	$ 24,624
Gross Unrealized gains After 10 years	0	0
Gross Unrealized losses After 10 years	149	116
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 21,264	$ 24,508
Weighted-average yield After 10 years	0.65%	2.00%
Puerto Rico government obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 5 to 10 years		$ 4,000
Gross Unrealized gains After 5 to 10 years		348
Gross Unrealized losses After 5 to 10 years		0
Fair value After 5 to 10 years		$ 4,348
Weighted-average yield After 5 to 10 years		5.12%
Amortized cost After 10 years	$ 3,987	$ 4,166
Gross Unrealized gains After 10 years	0	0
Gross Unrealized losses After 10 years	780	1,192
Allowance for Credit Losses After 10 years	308
Fair value After 10 years	$ 2,899	$ 2,974
Weighted-average yield After 10 years	6.97%	6.97%
Allowance for Credit Losses	$ 308	$ 0
United States And Puerto Rico Government Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	1,190,433	339,844
Gross unrealized gain	2,014	1,293
Gross unrealized loss	1,566	1,616
Allowance for Credit Losses	308
Fair value	$ 1,190,573	$ 339,521
Weighted-average yield	0.72%	2.11%
MBS [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 3,393,768	$ 1,768,664
Gross unrealized gain	66,981	23,280
Gross unrealized loss	3,951	8,440
Allowance for Credit Losses	1,002
Fair value	$ 3,455,796	$ 1,783,504
Weighted-average yield	1.47%	2.60%
MBS [Member] | FHLMC [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 75
Gross Unrealized gains After 1 to 5 years	8
Gross Unrealized losses After 1 to 5 years	0
Allowance for Credit Losses After 1 to 5 years	0
Fair value After 1 to 5 years	$ 83
Weighted-average yield After 1 to 5 years	4.86%
Amortized cost After 5 to 10 years	$ 60,773	$ 81,418
Gross Unrealized gains After 5 to 10 years	2,850	589
Gross Unrealized losses After 5 to 10 years	0	228
Allowance for Credit Losses After 5 to 10 years	0
Fair value After 5 to 10 years	$ 63,623	$ 81,779
Weighted-average yield After 5 to 10 years	2.15%	2.16%
Amortized cost After 10 years	$ 1,070,984	$ 424,316
Gross Unrealized gains After 10 years	15,340	3,873
Gross Unrealized losses After 10 years	159	758
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 1,086,165	$ 427,431
Weighted-average yield After 10 years	1.38%	2.50%
Amortized cost	$ 1,131,832	$ 505,734
Gross unrealized gain	18,198	4,462
Gross unrealized loss	159	986
Allowance for Credit Losses	0
Fair value	$ 1,149,871	$ 509,210
Weighted-average yield	1.42%	2.44%
MBS [Member] | GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year	$ 1
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	$ 1
Weighted-average yield Due within one year	1.93%
Amortized cost After 1 to 5 years	$ 26,918	$ 4,357
Gross Unrealized gains After 1 to 5 years	1,080	45
Gross Unrealized losses After 1 to 5 years	0	0
Allowance for Credit Losses After 1 to 5 years	0
Fair value After 1 to 5 years	$ 27,998	$ 4,402
Weighted-average yield After 1 to 5 years	2.91%	3.26%
Amortized cost After 5 to 10 years	$ 40,727	$ 42,303
Gross Unrealized gains After 5 to 10 years	128	607
Gross Unrealized losses After 5 to 10 years	69	0
Allowance for Credit Losses After 5 to 10 years	0
Fair value After 5 to 10 years	$ 40,786	$ 42,910
Weighted-average yield After 5 to 10 years	0.42%	2.77%
Amortized cost After 10 years	$ 614,584	$ 258,944
Gross Unrealized gains After 10 years	16,271	7,126
Gross Unrealized losses After 10 years	148	500
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 630,707	$ 265,570
Weighted-average yield After 10 years	1.27%	3.03%
Amortized cost	$ 682,230	$ 305,604
Gross unrealized gain	17,479	7,778
Gross unrealized loss	217	500
Allowance for Credit Losses	0
Fair value	$ 699,492	$ 312,882
Weighted-average yield	1.29%	3.00%
MBS [Member] | FNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 24,812	$ 19,779
Gross Unrealized gains After 1 to 5 years	891	415
Gross Unrealized losses After 1 to 5 years	0	3
Allowance for Credit Losses After 1 to 5 years	0
Fair value After 1 to 5 years	$ 25,703	$ 20,191
Weighted-average yield After 1 to 5 years	2.81%	2.79%
Amortized cost After 5 to 10 years	$ 110,832	$ 140,599
Gross Unrealized gains After 5 to 10 years	5,783	1,257
Gross Unrealized losses After 5 to 10 years	0	641
Allowance for Credit Losses After 5 to 10 years	0
Fair value After 5 to 10 years	$ 116,615	$ 141,215
Weighted-average yield After 5 to 10 years	2.13%	2.14%
Amortized cost After 10 years	$ 1,154,707	$ 700,213
Gross Unrealized gains After 10 years	23,459	9,006
Gross Unrealized losses After 10 years	203	1,208
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 1,177,963	$ 708,011
Weighted-average yield After 10 years	1.53%	2.58%
Amortized cost	$ 1,290,351	$ 860,591
Gross unrealized gain	30,133	10,678
Gross unrealized loss	203	1,852
Allowance for Credit Losses	0
Fair value	$ 1,320,281	$ 869,417
Weighted-average yield	1.61%	2.51%
MBS [Member] | Collateralized mortgage obligations guaranteed by FHLMC, FNMA and GNMA [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 538	$ 608
Gross Unrealized gains After 1 to 5 years	0	0
Gross Unrealized losses After 1 to 5 years	1	1
Allowance for Credit Losses After 1 to 5 years	0
Fair value After 1 to 5 years	$ 537	$ 607
Weighted-average yield After 1 to 5 years	0.81%	2.43%
Amortized cost After 5 to 10 years	$ 18,438
Gross Unrealized gains After 5 to 10 years	152
Gross Unrealized losses After 5 to 10 years	0
Allowance for Credit Losses After 5 to 10 years	0
Fair value After 5 to 10 years	$ 18,590
Weighted-average yield After 5 to 10 years	0.80%
Amortized cost After 10 years	$ 258,069	$ 80,130
Gross Unrealized gains After 10 years	1,019	362
Gross Unrealized losses After 10 years	491	220
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 258,597	$ 80,272
Weighted-average yield After 10 years	1.56%	2.76%
Amortized cost	$ 277,045	$ 80,738
Gross unrealized gain	1,171	362
Gross unrealized loss	492	221
Allowance for Credit Losses	0
Fair value	$ 277,724	$ 80,879
Weighted-average yield	1.51%	2.75%
MBS [Member] | Private label [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 10 years	$ 12,310	$ 15,997
Gross Unrealized gains After 10 years	0	0
Gross Unrealized losses After 10 years	2,880	4,881
Allowance for Credit Losses After 10 years	1,002
Fair value After 10 years	$ 8,428	$ 11,116
Weighted-average yield After 10 years	2.25%	3.90%
Gross unrealized loss	$ 3,900
Allowance for Credit Losses	1,002	$ 0
Fair value	$ 8,400
Weighted-average yield	2.25%
Other Debt Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 650	500
Gross Unrealized gains After 1 to 5 years	0	0
Gross Unrealized losses After 1 to 5 years	0	0
Allowance for Credit Losses After 1 to 5 years	0
Fair value After 1 to 5 years	$ 650	$ 500
Weighted-average yield After 1 to 5 years	2.94%	2.95%