INVESTMENT SECURITIES - Investment Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,798,373	$ 1,975,230
Noncredit Loss Component of OTTI Recorded in OCI	5,357	5,426
Gross Unrealized gain	19,542	7,260
Gross Unrealized loss	8,870	34,496
Investment securities available for sale	$ 1,803,688	$ 1,942,568
Weighted-average yield	2.53%	2.55%
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted-average yield	4.39%
U S Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost Due within one year	$ 7,452	$ 7,489
Noncredit Loss Component of OTTI Recorded in OCI Due within one year	0	0
Gross Unrealized gains Due within one year	12	0
Gross Unrealized losses Due within one year	0	33
Fair value Due within one year	$ 7,464	$ 7,456
Weighted-average yield Due within one year	2.42%	1.29%
U.S. government-sponsored agencies obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost Due within one year	$ 182,408	$ 191,531
Noncredit Loss Component of OTTI Recorded in OCI Due within one year	0	0
Gross Unrealized gains Due within one year	1	0
Gross Unrealized losses Due within one year	482	1,908
Fair value Due within one year	$ 181,927	$ 189,623
Weighted-average yield Due within one year	1.31%	1.28%
Amortized cost After 1 to 5 years	$ 166,618	$ 184,851
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0	0
Gross Unrealized gains After 1 to 5 years	580	203
Gross Unrealized losses After 1 to 5 years	473	2,249
Fair value After 1 to 5 years	$ 166,725	$ 182,805
Weighted-average yield After 1 to 5 years	2.02%	2.07%
Amortized cost After 5 to 10 years	$ 154,368	$ 195,750
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	1,064	286
Fair value After 5 to 10 years	$ 155,424	$ 194,362
Weighted-average yield After 5 to 10 years	2.89%	2.95%
Amortized cost After 10 years	$ 29,233	$ 34,627
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	6	0
Gross Unrealized losses After 10 years	60	217
Fair value After 10 years	$ 29,179	$ 34,410
Weighted-average yield After 10 years	2.70%	2.68%
Gross Unrealized losses After 5 to 10 years	$ 8	$ 1,674
Puerto Rico Government obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost After 5 to 10 years	4,000	4,000
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	92	128
Fair value After 5 to 10 years	$ 4,092	$ 4,128
Weighted-average yield After 5 to 10 years	5.12%	5.12%
Amortized cost After 10 years	$ 4,298	$ 4,185
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	0	0
Gross Unrealized losses After 10 years	1,399	1,361
Fair value After 10 years	$ 2,899	$ 2,824
Weighted-average yield After 10 years	6.97%	6.97%
Gross Unrealized losses After 5 to 10 years	$ 0	$ 0
United States And Puerto Rico Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	548,377	622,433
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross Unrealized gain	1,755	617
Gross Unrealized loss	2,422	7,442
Investment securities available for sale	$ 547,710	$ 615,608
Weighted-average yield	2.13%	2.18%
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,249,496	$ 1,352,297
Noncredit Loss Component of OTTI Recorded in OCI	5,357	5,426
Gross Unrealized gain	17,787	6,643
Gross Unrealized loss	6,448	27,054
Investment securities available for sale	$ 1,255,478	$ 1,326,460
Weighted-average yield	2.71%	2.71%
Mortgage Backed Securities [Member] | Freddie Mac (FHLMC) certificates [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost After 5 to 10 years	$ 83,358	$ 92,149
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	312	31
Fair value After 5 to 10 years	$ 83,339	$ 90,330
Weighted-average yield After 5 to 10 years	2.08%	2.09%
Amortized cost After 10 years	$ 246,050	$ 265,624
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	2,657	523
Gross Unrealized losses After 10 years	1,501	6,699
Fair value After 10 years	$ 247,206	$ 259,448
Weighted-average yield After 10 years	2.52%	2.52%
Amortized cost	$ 329,408	$ 357,773
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross Unrealized gain	2,969	554
Gross Unrealized loss	1,832	8,549
Investment securities available for sale	330,545	349,778
Gross Unrealized losses After 5 to 10 years	$ 331	$ 1,850
Weighted-average yield	2.41%	2.41%
Mortgage Backed Securities [Member] | Ginnie Mae (GNMA) certificates [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost Due within one year	$ 2
Noncredit Loss Component of OTTI Recorded in OCI Due within one year	0
Gross Unrealized gains Due within one year	0
Gross Unrealized losses Due within one year	0
Fair value Due within one year	$ 2
Weighted-average yield Due within one year	3.77%
Amortized cost After 1 to 5 years	$ 137	$ 176
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0	0
Gross Unrealized gains After 1 to 5 years	2	3
Gross Unrealized losses After 1 to 5 years	0	0
Fair value After 1 to 5 years	$ 139	$ 179
Weighted-average yield After 1 to 5 years	3.84%	3.43%
Amortized cost After 5 to 10 years	$ 54,179	$ 61,604
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	480	408
Fair value After 5 to 10 years	$ 54,624	$ 61,509
Weighted-average yield After 5 to 10 years	2.87%	2.88%
Amortized cost After 10 years	$ 111,034	$ 118,898
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	5,455	2,938
Gross Unrealized losses After 10 years	187	747
Fair value After 10 years	$ 116,302	$ 121,089
Weighted-average yield After 10 years	3.94%	3.92%
Amortized cost	$ 165,352	$ 180,678
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross Unrealized gain	5,937	3,349
Gross Unrealized loss	222	1,250
Investment securities available for sale	171,067	182,777
Gross Unrealized losses After 5 to 10 years	$ 35	$ 503
Weighted-average yield	3.59%	3.56%
Mortgage Backed Securities [Member] | Fannie Mae (FNMA) certificates [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost Due within one year		$ 119
Noncredit Loss Component of OTTI Recorded in OCI Due within one year		0
Gross Unrealized gains Due within one year		2
Gross Unrealized losses Due within one year		0
Fair value Due within one year		$ 121
Weighted-average yield Due within one year		2.20%
Amortized cost After 1 to 5 years	$ 19,789	$ 19,798
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0	0
Gross Unrealized gains After 1 to 5 years	402	50
Gross Unrealized losses After 1 to 5 years	6	122
Fair value After 1 to 5 years	$ 20,185	$ 19,726
Weighted-average yield After 1 to 5 years	2.79%	2.79%
Amortized cost After 5 to 10 years	$ 149,405	$ 165,067
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	1,254	2
Fair value After 5 to 10 years	$ 149,823	$ 161,247
Weighted-average yield After 5 to 10 years	2.12%	2.13%
Amortized cost After 10 years	$ 509,874	$ 543,972
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	6,813	2,211
Gross Unrealized losses After 10 years	3,551	13,233
Fair value After 10 years	$ 513,136	$ 532,950
Weighted-average yield After 10 years	2.67%	2.67%
Amortized cost	$ 679,068	$ 728,956
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross Unrealized gain	8,469	2,265
Gross Unrealized loss	4,393	17,177
Investment securities available for sale	683,144	714,044
Gross Unrealized losses After 5 to 10 years	$ 836	$ 3,822
Weighted-average yield	2.55%	2.55%
Mortgage Backed Securities [Member] | Collateralized mortgage obligations guaranteed by the FHLMC and GNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 930	$ 6,530
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0	0
Gross Unrealized gains After 1 to 5 years	1	1
Gross Unrealized losses After 1 to 5 years	0	18
Fair value After 1 to 5 years	$ 931	$ 6,513
Weighted-average yield After 1 to 5 years	3.07%	3.15%
Amortized cost After 10 years	$ 56,874	$ 59,020
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	411	474
Gross Unrealized losses After 10 years	1	60
Fair value After 10 years	$ 57,284	$ 59,434
Weighted-average yield After 10 years	3.16%	3.22%
Amortized cost	$ 57,804	$ 65,550
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross Unrealized gain	412	475
Gross Unrealized loss	1	78
Investment securities available for sale	$ 58,215	$ 65,947
Weighted-average yield	3.16%	3.22%
Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost After 10 years	$ 17,864	$ 19,340
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	5,357	5,426
Gross Unrealized gains After 10 years	0	0
Gross Unrealized losses After 10 years	0	0
Fair value After 10 years	$ 12,507	$ 13,914
Weighted-average yield After 10 years	4.39%	4.89%
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 500	$ 500
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0	0
Gross Unrealized gains After 1 to 5 years	0	0
Gross Unrealized losses After 1 to 5 years	0	0
Fair value After 1 to 5 years	$ 500	$ 500
Weighted-average yield After 1 to 5 years	2.96%	2.96%