INVESTMENT SECURITIES - Roll-Forward of Credit Losses on Debt Securities Held by Corporation (Detail) - Available-for-sale Securities [Member] - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Beginning balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	$ 6,792	$ 28,981	$ 22,294
Credit impairments recognized in earnings on securities that have been previously impaired	50	12,231	6,687
Credit loss reductions for securities sold during the period	0	(34,420)	0
Ending balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	6,842	6,792	28,981
Puerto Rico-government obligations [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Beginning balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	0	22,189	15,889
Credit impairments recognized in earnings on securities that have been previously impaired		12,231	6,300
Credit loss reductions for securities sold during the period		(34,420)	0
Ending balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI		0	22,189
Private label MBS [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Beginning balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	6,792	6,792	6,405
Credit impairments recognized in earnings on securities that have been previously impaired	50	0	387
Credit loss reductions for securities sold during the period	0	0	0
Ending balance of credit losses on debt securities held for which a portion of an OTTI was recognized in OCI	$ 6,842	$ 6,792	$ 6,792

This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which a previous OTTI was recognized and the investor does not intend to sell the debt security and it is not more likely than not that the investor will be required to sell the debt security before recovery of its amortized cost basis.

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- Definition

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security because of the sale of impaired securities during the period.

+ References

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