INVESTMENT SECURITIES - Investment Securities Available for Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 3,242,955		$ 2,109,008
Gross Unrealized gain	60,021		24,573
Gross Unrealized loss	6,941		10,056
Allowance for Credit Losses	1,386	$ 1,631	0
Investment securities available for sale	$ 3,294,649		$ 2,123,525
Weighted-average yield	1.60%		2.52%
U S Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost Due within one year	$ 7,493
Gross Unrealized gains Due within one year	38
Gross Unrealized losses Due within one year	0
Allowance for Credit Losses within one year	0
Fair value Due within one year	$ 7,531
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 obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost Due within one year	$ 34,442		$ 93,299
Gross Unrealized gains Due within one year	402		103
Gross Unrealized losses Due within one year	0		106
Allowance for Credit Losses within one year	0
Fair value Due within one year	$ 34,844		$ 93,296
Weighted-average yield Due within one year	1.82%		1.67%
Amortized cost After 1 to 5 years	$ 544,175		$ 142,513
Gross Unrealized gains After 1 to 5 years	813		676
Gross Unrealized losses After 1 to 5 years	958		52
Allowance for Credit Losses After 1 to 5 years	0
Fair value After 1 to 5 years	$ 544,030		$ 143,137
Weighted-average yield After 1 to 5 years	0.80%		2.12%
Amortized cost After 5 to 10 years	$ 117,940		$ 63,764
Gross Unrealized gains After 5 to 10 years	671		165
Gross Unrealized losses After 5 to 10 years	181		150
Allowance for Credit Losses After 5 to 10 years	0
Fair value After 5 to 10 years	$ 118,430		$ 63,779
Weighted-average yield After 5 to 10 years	1.41%		2.33%
Amortized cost After 10 years	$ 21,820		$ 24,624
Gross Unrealized gains After 10 years	0		0
Gross Unrealized losses After 10 years	144		116
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 21,676		$ 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		$ 4,000
Gross Unrealized gains After 5 to 10 years	16		348
Gross Unrealized losses After 5 to 10 years	0		0
Allowance for Credit Losses After 5 to 10 years	0
Fair value After 5 to 10 years	$ 4,016		$ 4,348
Weighted-average yield After 5 to 10 years	5.12%		5.12%
Amortized cost After 10 years	$ 4,043		$ 4,166
Gross Unrealized gains After 10 years	0		0
Gross Unrealized losses After 10 years	828		1,192
Allowance for Credit Losses After 10 years	308
Fair value After 10 years	$ 2,907		$ 2,974
Weighted-average yield After 10 years	6.97%		6.97%
Allowance for Credit Losses	$ 308	308	$ 0
Investment securities available for sale	6,900
United States And Puerto Rico Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	733,913		339,844
Gross Unrealized gain	1,940		1,293
Gross Unrealized loss	2,111		1,616
Allowance for Credit Losses	308
Investment securities available for sale	$ 733,434		$ 339,521
Weighted-average yield	1.01%		2.11%
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 2,508,392		$ 1,768,664
Gross Unrealized gain	58,081		23,280
Gross Unrealized loss	4,830		8,440
Allowance for Credit Losses	1,078
Investment securities available for sale	$ 2,560,565		$ 1,783,504
Weighted-average yield	1.77%		2.60%
Mortgage Backed Securities [Member] | FHLMC [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost Due within one year	$ 83
Gross Unrealized gains Due within one year	8
Gross Unrealized losses Due within one year	0
Allowance for Credit Losses within one year	0
Fair value Due within one year	$ 91
Weighted-average yield Due within one year	4.86%
Amortized cost After 5 to 10 years	$ 66,337		$ 81,418
Gross Unrealized gains After 5 to 10 years	2,939		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	$ 69,276		$ 81,779
Weighted-average yield After 5 to 10 years	2.15%		2.16%
Amortized cost After 10 years	$ 579,684		$ 424,316
Gross Unrealized gains After 10 years	12,331		3,873
Gross Unrealized losses After 10 years	139		758
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 591,876		$ 427,431
Weighted-average yield After 10 years	1.73%		2.50%
Amortized cost	$ 646,104		$ 505,734
Gross Unrealized gain	15,278		4,462
Gross Unrealized loss	139		986
Allowance for Credit Losses	0
Investment securities available for sale	$ 661,243		$ 509,210
Weighted-average yield	1.77%		2.44%
Mortgage Backed Securities [Member] | GNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 29,736		$ 4,357
Gross Unrealized gains After 1 to 5 years	1,141		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	$ 30,877		$ 4,402
Weighted-average yield After 1 to 5 years	2.92%		3.26%
Amortized cost After 5 to 10 years	$ 44,804		$ 42,303
Gross Unrealized gains After 5 to 10 years	121		607
Gross Unrealized losses After 5 to 10 years	107		0
Allowance for Credit Losses After 5 to 10 years	0
Fair value After 5 to 10 years	$ 44,818		$ 42,910
Weighted-average yield After 5 to 10 years	0.61%		2.77%
Amortized cost After 10 years	$ 690,171		$ 258,944
Gross Unrealized gains After 10 years	13,154		7,126
Gross Unrealized losses After 10 years	330		500
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 702,995		$ 265,570
Weighted-average yield After 10 years	1.52%		3.03%
Amortized cost	$ 764,713		$ 305,604
Gross Unrealized gain	14,416		7,778
Gross Unrealized loss	437		500
Allowance for Credit Losses	0
Investment securities available for sale	$ 778,692		$ 312,882
Weighted-average yield	1.52%		3.00%
Mortgage Backed Securities [Member] | FNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 24,823		$ 19,779
Gross Unrealized gains After 1 to 5 years	1,159		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	$ 25,982		$ 20,191
Weighted-average yield After 1 to 5 years	2.80%		2.79%
Amortized cost After 5 to 10 years	$ 114,332		$ 140,599
Gross Unrealized gains After 5 to 10 years	5,882		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	$ 120,214		$ 141,215
Weighted-average yield After 5 to 10 years	2.12%		2.14%
Amortized cost After 10 years	$ 709,800		$ 700,213
Gross Unrealized gains After 10 years	19,848		9,006
Gross Unrealized losses After 10 years	399		1,208
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 729,249		$ 708,011
Weighted-average yield After 10 years	1.95%		2.58%
Amortized cost	$ 848,955		$ 860,591
Gross Unrealized gain	26,889		10,678
Gross Unrealized loss	399		1,852
Allowance for Credit Losses	0
Investment securities available for sale	$ 875,445		$ 869,417
Weighted-average yield	2.00%		2.51%
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]
Amortized cost After 1 to 5 years	$ 581		$ 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	$ 580		$ 607
Weighted-average yield After 1 to 5 years	0.82%		2.43%
Amortized cost After 5 to 10 years	$ 20,055
Gross Unrealized gains After 5 to 10 years	123
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	$ 20,178
Weighted-average yield After 5 to 10 years	0.80%
Amortized cost After 10 years	$ 214,437		$ 80,130
Gross Unrealized gains After 10 years	1,375		362
Gross Unrealized losses After 10 years	224		220
Allowance for Credit Losses After 10 years	0
Fair value After 10 years	$ 215,588		$ 80,272
Weighted-average yield After 10 years	1.87%		2.76%
Amortized cost	$ 235,073		$ 80,738
Gross Unrealized gain	1,498		362
Gross Unrealized loss	225		221
Allowance for Credit Losses	0
Investment securities available for sale	$ 236,346		$ 80,879
Weighted-average yield	1.77%		2.75%
Mortgage Backed Securities [Member] | Private label [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost After 10 years	$ 13,547		$ 15,997
Gross Unrealized gains After 10 years	0		0
Gross Unrealized losses After 10 years	3,630		4,881
Allowance for Credit Losses After 10 years	1,078
Fair value After 10 years	$ 8,839		$ 11,116
Weighted-average yield After 10 years	2.22%		3.90%
Gross Unrealized loss	$ 4,700
Allowance for Credit Losses	1,078	$ 1,323	$ 0
Investment securities available for sale	8,800
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%