INVESTMENT SECURITIES - Roll-Forward of Credit Losses on Debt Securities Held by Corporation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Credit losses at beginning of the period	$ 22,294	$ 5,777
Additions:
Credit losses on debt securities for which an OTTI was no previously recognized	0	15,889
Credit losses on debt securities for which an OTTI was previously recognized	6,687	628
Reductions:
Ending balance of credit losses	28,981	22,294	$ 5,777
Puerto Rico Government Obligations [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Credit losses at beginning of the period	15,889	0
Additions:
Credit losses on debt securities for which an OTTI was no previously recognized	0	15,889
Credit losses on debt securities for which an OTTI was previously recognized	6,300	0
Reductions:
Ending balance of credit losses	22,189	15,889	0
Mortgage Backed Securities Issued By Private Enterprises [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Credit losses at beginning of the period	6,405	5,777	5,389
Additions:
Credit losses on debt securities for which an OTTI was no previously recognized	0	0	0
Credit losses on debt securities for which an OTTI was previously recognized	387	628	388
Reductions:
Ending balance of credit losses	$ 6,792	$ 6,405	$ 5,777