INVESTMENT SECURITIES - Debt Securities Held-to-Maturity by Credit Quality Indicator (Detail) - Municipal Bonds [Member] - PUERTO RICO - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Held To Maturity Securities [Line Items]
Held to Maturity Amortized cost	$ 189,156	$ 138,675
Pass [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to Maturity Amortized cost	189,156	138,675
Special Mention [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to Maturity Amortized cost	0	0
Substandard [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to Maturity Amortized cost	0	0
Doubtful [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to Maturity Amortized cost	0	0
Loss [Member]
Schedule Of Held To Maturity Securities [Line Items]
Held to Maturity Amortized cost	$ 0	$ 0