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INVESTMENT SECURITIES - Investment Securities Held to Maturity (Securities in continous unrealized loss position) (Detail) - Nontaxable Municipal Bonds [Member] - Puerto Rico [Member] - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Schedule Of Held To Maturity Securities [Line Items]    
Fair value less than 12 months $ 0 $ 0
Unrealized losses less than 12 months 0 0
Fair value 12 months or more 131,032 132,759
Unrealized losses 12 months or more 19,595 23,431
Total fair value 131,032 132,759
Total unrealized losses $ 19,595 $ 23,431