INVESTMENT SECURITIES - Investment Securities Available for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 1,975,230	$ 1,903,878
Noncredit Loss Component of OTTI Recorded in OCI	5,426	5,731
Gross unrealized gain	7,260	11,309
Gross unrealized loss	34,496	18,440
Fair value	$ 1,942,568	$ 1,891,016
Weighted-average yield	2.55%	2.27%
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost		$ 424
Noncredit Loss Component of OTTI Recorded in OCI		0
Gross unrealized gain		0
Gross unrealized loss		6
Fair value		$ 418
Weighted-average yield		2.11%
U.S. Treasury securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year	$ 7,489
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	33
Fair value Due within one year	$ 7,456
Weighted-average yield Due within one year	1.29%
Amortized cost After 1 to 5 years		$ 7,458
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years		0
Gross Unrealized gains After 1 to 5 years		0
Gross Unrealized losses After 1 to 5 years		57
Fair value After 1 to 5 years		$ 7,401
Weighted-average yield After 1 to 5 years		1.29%
U.S. government-sponsored agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year	$ 191,531	$ 122,471
Noncredit Loss Component of OTTI Recorded in OCI Due within one year	0	0
Gross Unrealized gains Due within one year	0	0
Gross Unrealized losses Due within one year	1,908	319
Fair value Due within one year	$ 189,623	$ 122,152
Weighted-average yield Due within one year	1.28%	1.06%
Amortized cost After 1 to 5 years	$ 184,851	$ 309,472
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0	0
Gross Unrealized gains After 1 to 5 years	203	28
Gross Unrealized losses After 1 to 5 years	2,249	3,735
Fair value After 1 to 5 years	$ 182,805	$ 305,765
Weighted-average yield After 1 to 5 years	2.07%	1.42%
Amortized cost After 5 to 10 years	$ 195,750	$ 133,451
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	286	117
Gross Unrealized losses After 5 to 10 years	1,674	319
Fair value After 5 to 10 years	$ 194,362	$ 133,249
Weighted-average yield After 5 to 10 years	2.95%	2.72%
Amortized cost After 10 years	$ 34,627	$ 40,769
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	0	1
Gross Unrealized losses After 10 years	217	149
Fair value After 10 years	$ 34,410	$ 40,621
Weighted-average yield After 10 years	2.68%	1.84%
Puerto Rico-government obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 5 to 10 years	$ 4,000	$ 4,071
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	128	47
Gross Unrealized losses After 5 to 10 years	0	0
Fair value After 5 to 10 years	$ 4,128	$ 4,118
Weighted-average yield After 5 to 10 years	5.12%	3.14%
Amortized cost After 10 years	$ 4,185	$ 3,972
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	1,361	1,277
Fair value After 10 years	$ 2,824	$ 2,695
Weighted-average yield After 10 years	6.97%	6.97%
United States And Puerto Rico Government Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 622,433	$ 621,664
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross unrealized gain	617	193
Gross unrealized loss	7,442	5,856
Fair value	$ 615,608	$ 616,001
Weighted-average yield	2.18%	1.70%
Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost	$ 1,352,297	$ 1,281,690
Noncredit Loss Component of OTTI Recorded in OCI	5,426	5,731
Gross unrealized gain	6,643	11,116
Gross unrealized loss	27,054	12,578
Fair value	$ 1,326,460	$ 1,274,497
Weighted-average yield	2.71%	2.54%
Mortgage Backed Securities [Member] | Freddie Mac (FHLMC) certificates [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 5 to 10 years	$ 92,149	$ 18,658
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	31	14
Gross Unrealized losses After 5 to 10 years	1,850	63
Fair value After 5 to 10 years	$ 90,330	$ 18,609
Weighted-average yield After 5 to 10 years	2.09%	2.14%
Amortized cost After 10 years	$ 265,624	$ 297,733
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	523	217
Gross Unrealized losses After 10 years	6,699	4,853
Fair value After 10 years	$ 259,448	$ 293,097
Weighted-average yield After 10 years	2.52%	2.23%
Amortized cost	$ 357,773	$ 316,391
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross unrealized gain	554	231
Gross unrealized loss	8,549	4,916
Fair value	$ 349,778	$ 311,706
Weighted-average yield	2.41%	2.23%
Mortgage Backed Securities [Member] | Ginnie Mae (GNMA) certificates [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 176	$ 81
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0	0
Gross Unrealized gains After 1 to 5 years	3	1
Gross Unrealized losses After 1 to 5 years	0	0
Fair value After 1 to 5 years	$ 179	$ 82
Weighted-average yield After 1 to 5 years	3.43%	3.23%
Amortized cost After 5 to 10 years	$ 61,604	$ 69,661
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	408	1,244
Gross Unrealized losses After 5 to 10 years	503	0
Fair value After 5 to 10 years	$ 61,509	$ 70,905
Weighted-average yield After 5 to 10 years	2.88%	3.05%
Amortized cost After 10 years	$ 118,898	$ 145,067
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	2,938	5,910
Gross Unrealized losses After 10 years	747	334
Fair value After 10 years	$ 121,089	$ 150,643
Weighted-average yield After 10 years	3.92%	3.81%
Amortized cost	$ 180,678	$ 214,809
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross unrealized gain	3,349	7,155
Gross unrealized loss	1,250	334
Fair value	$ 182,777	$ 221,630
Weighted-average yield	3.56%	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	$ 19,798	$ 20,831
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0	0
Gross Unrealized gains After 1 to 5 years	50	294
Gross Unrealized losses After 1 to 5 years	122	109
Fair value After 1 to 5 years	$ 19,726	$ 21,016
Weighted-average yield After 1 to 5 years	2.79%	2.69%
Amortized cost After 5 to 10 years	$ 165,067	$ 49,934
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years	0	0
Gross Unrealized gains After 5 to 10 years	2	0
Gross Unrealized losses After 5 to 10 years	3,822	818
Fair value After 5 to 10 years	$ 161,247	$ 49,116
Weighted-average yield After 5 to 10 years	2.13%	1.83%
Amortized cost After 10 years	$ 543,972	$ 613,129
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	2,211	3,180
Gross Unrealized losses After 10 years	13,233	6,401
Fair value After 10 years	$ 532,950	$ 609,908
Weighted-average yield After 10 years	2.67%	2.43%
Amortized cost	$ 728,956	$ 683,894
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross unrealized gain	2,265	3,474
Gross unrealized loss	17,177	7,328
Fair value	$ 714,044	$ 680,040
Weighted-average yield	2.55%	2.39%
Mortgage Backed Securities [Member] | Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 1 to 5 years	$ 6,530	$ 5,918
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0	0
Gross Unrealized gains After 1 to 5 years	1	14
Gross Unrealized losses After 1 to 5 years	18	0
Fair value After 1 to 5 years	$ 6,513	$ 5,932
Weighted-average yield After 1 to 5 years	3.15%	2.21%
Amortized cost After 5 to 10 years		$ 2,556
Noncredit Loss Component of OTTI Recorded in OCI After 5 to 10 years		0
Gross Unrealized gains After 5 to 10 years		11
Gross Unrealized losses After 5 to 10 years		0
Fair value After 5 to 10 years		$ 2,567
Weighted-average yield After 5 to 10 years		2.23%
Amortized cost After 10 years	$ 59,020	$ 35,331
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	0	0
Gross Unrealized gains After 10 years	474	231
Gross Unrealized losses After 10 years	60	0
Fair value After 10 years	$ 59,434	$ 35,562
Weighted-average yield After 10 years	3.22%	2.22%
Amortized cost	$ 65,550	$ 43,805
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross unrealized gain	475	256
Gross unrealized loss	78	0
Fair value	$ 65,947	$ 44,061
Weighted-average yield	3.22%	2.22%
Mortgage Backed Securities [Member] | Other mortgage pass-through trust certificates [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost After 10 years	$ 19,340	$ 22,791
Noncredit Loss Component of OTTI Recorded in OCI After 10 years	5,426	5,731
Gross Unrealized gains After 10 years	0	0
Gross Unrealized losses After 10 years	0	0
Fair value After 10 years	$ 13,914	$ 17,060
Weighted-average yield After 10 years	4.89%	2.44%
Amortized cost	$ 19,340	$ 22,791
Noncredit Loss Component of OTTI Recorded in OCI	5,426	5,731
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value	$ 13,914	$ 17,060
Weighted-average yield	4.89%	2.44%
Other Debt Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year		$ 100
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		$ 100
Weighted-average yield Due within one year		1.48%
Amortized cost After 1 to 5 years	$ 500
Noncredit Loss Component of OTTI Recorded in OCI After 1 to 5 years	0
Gross Unrealized gains After 1 to 5 years	0
Gross Unrealized losses After 1 to 5 years	0
Fair value After 1 to 5 years	$ 500
Weighted-average yield After 1 to 5 years	2.96%
Amortized cost	$ 500	$ 100
Noncredit Loss Component of OTTI Recorded in OCI	0	0
Gross unrealized gain	0	0
Gross unrealized loss	0	0
Fair value	$ 500	$ 100
Weighted-average yield	2.96%	1.48%