INVESTMENT SECURITIES - Available-For-Sale Investments' Fair Value And Gross Unrealized Losses (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	$ 1,100,920	$ 1,331,998
Unrealized Losses Less than 12 months	13,535	19,090
Fair Value 12 months or more	48,456	43,302
Unrealized Losses 12 months or more	9,224	24,034
Total Fair Value	1,149,376	1,375,300
Total Unrealized Losses	22,759	43,124
Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	410	408
Unrealized Losses Less than 12 months	4	7
Fair Value 12 months or more	0	0
Unrealized Losses 12 months or more	0	0
Total Fair Value	410	408
Total Unrealized Losses	4	7
Debt Securities [Member] | Puerto Rico Government Obligations [Member]
Schedule Of Available For Sale 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	1,470	22,609
Unrealized Losses 12 months or more	2,402	15,912
Total Fair Value	1,470	22,609
Total Unrealized Losses	2,402	15,912
Debt Securities [Member] | US States And Political Subdivisions Member [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	422,548	469,046
Unrealized Losses Less than 12 months	2,234	3,334
Fair Value 12 months or more	27,918	0
Unrealized Losses 12 months or more	158	0
Total Fair Value	450,466	469,046
Total Unrealized Losses	2,392	3,334
Mortgage Backed Securities [Member] | Collateralized Mortgage Obligations Member
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months		55,309
Unrealized Losses Less than 12 months		163
Fair Value 12 months or more		0
Unrealized Losses 12 months or more		0
Total Fair Value		55,309
Total Unrealized Losses		163
Mortgage Backed Securities [Member] | Other-mortgage pass-through trust certificates [Member]
Schedule Of Available For Sale 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	18,201	20,693
Unrealized Losses 12 months or more	6,637	8,122
Total Fair Value	18,201	20,693
Total Unrealized Losses	6,637	8,122
Mortgage Backed Securities [Member] | Government National Mortgage Association Certificates And Obligations G N M A [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	798	43,388
Unrealized Losses Less than 12 months	21	92
Fair Value 12 months or more	0	0
Unrealized Losses 12 months or more	0	0
Total Fair Value	798	43,388
Total Unrealized Losses	21	92
Mortgage Backed Securities [Member] | Federal National Mortgage Association Certificates And Obligations F N M A [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	461,637	519,008
Unrealized Losses Less than 12 months	7,249	9,667
Fair Value 12 months or more	0	0
Unrealized Losses 12 months or more	0	0
Total Fair Value	461,637	519,008
Total Unrealized Losses	7,249	9,667
Mortgage Backed Securities [Member] | Federal Home Loan Mortgage Corporation Certificates And Obligations F H L M C [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair Value Less than 12 months	215,527	244,839
Unrealized Losses Less than 12 months	4,027	5,827
Fair Value 12 months or more	867	0
Unrealized Losses 12 months or more	27	0
Total Fair Value	216,394	244,839
Total Unrealized Losses	$ 4,054	$ 5,827