INVESTMENT SECURITIES - Aggregate amortized cost and approximate market value of investment securities available for sale by contractual maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Total Amortized cost	$ 1,975,230	$ 1,903,878
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Total Fair value	1,942,568	1,891,016
Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Total Amortized cost	1,352,297	1,281,690
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Total Fair value	1,326,460	1,274,497
United States And Puerto Rico Government Obligations [Member]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Total Amortized cost	622,433	621,664
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Total Fair value	615,608	$ 616,001
United States and Puerto Rico government obligations and other debt obligations [Member]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Total Amortized cost	622,933
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Total Fair value	616,108
Debt Securities [Member]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Amortized cost Due within one year	199,020
Amortized cost After 1 to 5 years	185,351
Amortized cost After 5 to 10 years	199,750
Amortized cost After 10 years	38,812
Total Amortized cost	1,975,230
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Fair value Due within one year	197,079
Fair value After 1 to 5 years	183,305
Fair value After 5 to 10 years	198,490
Fair value After 10 years	37,234
Total Fair value	$ 1,942,568

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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