INVESTMENT SECURITIES - Aggregate amortized cost and approximate market value of investment securities available for sale by contractual maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Total Amortized cost	$ 4,584,851	$ 2,109,008
Total Fair value	4,647,019	2,123,525
United States And Puerto Rico Government Obligations And Other Debt Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized cost Due within one year	31,911
Amortized cost After 1 to 5 years	692,318
Amortized cost After 5 to 10 years	441,454
Amortized cost After 10 years	25,400
Total Amortized cost	1,191,083
Fair value Due within one year	32,193
Fair value After 1 to 5 years	692,939
Fair value After 5 to 10 years	441,928
Fair value After 10 years	24,163
Total Fair value	1,191,223
Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Total Amortized cost	3,393,768	1,768,664
Total Fair value	$ 3,455,796	$ 1,783,504

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

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