Fair value and gross unrealized losses of investment securities available-for-sale, aggregated by investment category and length of time individual securities have been in a continuous unrealized loss position (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 341,051	$ 122,731	$ 735,986
Less than 12 months Gross Unrealized Losses	1,764	884	4,787
12 months or more Fair Value	52,974	45,807	55,961
12 months or more Gross Unrealized Losses	2,917	6,831	4,743
Total Fair Value	394,025	168,538	791,947
Total Gross Unrealized Losses	4,681	7,715	9,530
US Government Sponsored Enterprises Debt Securities Member
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	235,106	0	304,080
Less than 12 months Gross Unrealized Losses	1,327	0	1,531
12 months or more Fair Value	0	0	0
12 months or more Gross Unrealized Losses	0	0	0
Total Fair Value	235,106	0	304,080
Total Gross Unrealized Losses	1,327	0	1,531
Obligations of Puerto Rico, States and political subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	2,816	7,817	18,138
Less than 12 months Gross Unrealized Losses	23	28	167
12 months or more Fair Value	0	191	301
12 months or more Gross Unrealized Losses	0	3	6
Total Fair Value	2,816	8,008	18,439
Total Gross Unrealized Losses	23	31	173
Collateralized Mortgage Obligations Issued By U S Government Sponsored Enterprises And U S Government [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	101,959	90,543	345,887
Less than 12 months Gross Unrealized Losses	379	208	1,876
12 months or more Fair Value	3,002	0	0
12 months or more Gross Unrealized Losses	15	0	0
Total Fair Value	104,961	90,543	345,887
Total Gross Unrealized Losses	394	208	1,876
Collateralized Mortgage Obligations Issued By Private Enterprise [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	914	13,595	21,678
Less than 12 months Gross Unrealized Losses	29	539	252
12 months or more Fair Value	48,494	44,148	46,424
12 months or more Gross Unrealized Losses	2,860	6,783	4,385
Total Fair Value	49,408	57,743	68,102
Total Gross Unrealized Losses	2,889	7,322	4,637
Collateralized Mortgage Backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	209	5,577	35,010
Less than 12 months Gross Unrealized Losses	3	14	714
12 months or more Fair Value	1,475	1,466	9,185
12 months or more Gross Unrealized Losses	34	36	265
Total Fair Value	1,684	7,043	44,195
Total Gross Unrealized Losses	37	50	979
Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	47	5,199	3,798
Less than 12 months Gross Unrealized Losses	3	95	169
12 months or more Fair Value	3	2	51
12 months or more Gross Unrealized Losses	8	9	87
Total Fair Value	50	5,201	3,849
Total Gross Unrealized Losses	11	104	256
Other
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	0	7,395
Less than 12 months Gross Unrealized Losses	0	0	78
12 months or more Fair Value	0	0	0
12 months or more Gross Unrealized Losses	0	0	0
Total Fair Value	0	0	7,395
Total Gross Unrealized Losses	$ 0	$ 0	$ 78