Fair value and gross unrealized losses of investment securities held-to-maturity, 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	$ 0	$ 10,323	$ 26,407
Less than 12 months Gross Unrealized Losses	0	92	567
12 months or more Fair Value	30,866	31,213	30,969
12 months or more Gross Unrealized Losses	674	862	1,031
Total Fair Value	30,866	41,536	57,376
Total Gross Unrealized Losses	674	954	1,598
Obligations of Puerto Rico, States and political subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	10,323	26,407
Less than 12 months Gross Unrealized Losses	0	92	567
12 months or more Fair Value	30,866	31,062	30,808
12 months or more Gross Unrealized Losses	674	853	1,022
Total Fair Value	30,866	41,385	57,215
Total Gross Unrealized Losses	674	945	1,589
Collateralized Mortgage Obligations Issued By Private Enterprise [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	0	0
Less than 12 months Gross Unrealized Losses	0	0	0
12 months or more Fair Value	0	151	161
12 months or more Gross Unrealized Losses	0	9	9
Total Fair Value	0	151	161
Total Gross Unrealized Losses	0	9	9
US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	0	0
Less than 12 months Gross Unrealized Losses	0	0	0
12 months or more Fair Value	0	0	0
12 months or more Gross Unrealized Losses	0	0	0
Total Fair Value	0	0	0
Total Gross Unrealized Losses	0	0	0
Other
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	0	0
Less than 12 months Gross Unrealized Losses	0	0	0
12 months or more Fair Value	0	0	0
12 months or more Gross Unrealized Losses	0	0	0
Total Fair Value	0	0	0
Total Gross Unrealized Losses	$ 0	$ 0	$ 0