INVESTMENT SECURITIES - OTTI Losses on Available-for-Sale Debt Securities (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule Of Available For Sale Securities [Line Items]
Total other-than-temporary impairment losses		$ 0	$ 0	$ (12,231)	$ (1,845)
Credit losses on debt securities for which an OTTI was no previously recognized		0	0		0
Portion of loss previously recognized in other comprehensive income		0	0	0	(4,842)
Net impairment losses recognized in earnings	[1]	0	0	(12,231)	(6,687)
Mortgage Backed Securities Issued By Private Enterprises [Member]
Schedule Of Available For Sale Securities [Line Items]
Credit losses on debt securities for which an OTTI was no previously recognized		$ 0	0		0
Net impairment losses recognized in earnings					(400)
US States And Political Subdivisions Member [Member]
Schedule Of Available For Sale Securities [Line Items]
Credit losses on debt securities for which an OTTI was no previously recognized			$ 0		0
Net impairment losses recognized in earnings				$ (12,200)	$ (6,300)

[1] For the nine-month periods ended September 30, 2017 and 2016, approximately $12.2 million and $6.3 million, respectively, of the credit impairment recognized in earnings consisted of credit losses on Puerto Rico Government debt securities that were sold in the second quarter of 2017, as further discussed below. For the nine-month period ended September 30, 2016, $0.4 million of the credit impairment recognized in earnings was associated with credit losses on private label MBS.