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	Sep. 30, 2012	Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 267,185	$ 122,731
Less than 12 months Gross Unrealized Losses	1,561	884
12 months or more Fair Value	15,622	45,807
12 months or more Gross Unrealized Losses	1,191	6,831
Total Fair Value	282,807	168,538
Total Gross Unrealized Losses	2,752	7,715
US Government Sponsored Enterprises Debt Securities Member
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	46,248	0
Less than 12 months Gross Unrealized Losses	172	0
12 months or more Fair Value	0	0
12 months or more Gross Unrealized Losses	0	0
Total Fair Value	46,248	0
Total Gross Unrealized Losses	172	0
Puerto Rico States And Political Subdivisions Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	752	7,817
Less than 12 months Gross Unrealized Losses	9	28
12 months or more Fair Value	2,032	191
12 months or more Gross Unrealized Losses	33	3
Total Fair Value	2,784	8,008
Total Gross Unrealized Losses	42	31
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	218,129	90,543
Less than 12 months Gross Unrealized Losses	1,312	208
12 months or more Fair Value	2,491	0
12 months or more Gross Unrealized Losses	4	0
Total Fair Value	220,620	90,543
Total Gross Unrealized Losses	1,316	208
Collateralized Mortgage Obligations Issued By Private Enterprise [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	13,595
Less than 12 months Gross Unrealized Losses	0	539
12 months or more Fair Value	10,263	44,148
12 months or more Gross Unrealized Losses	1,106	6,783
Total Fair Value	10,263	57,743
Total Gross Unrealized Losses	1,106	7,322
Collateralized Mortgage Backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	204	5,577
Less than 12 months Gross Unrealized Losses	4	14
12 months or more Fair Value	787	1,466
12 months or more Gross Unrealized Losses	36	36
Total Fair Value	991	7,043
Total Gross Unrealized Losses	40	50
Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	1,852	5,199
Less than 12 months Gross Unrealized Losses	64	95
12 months or more Fair Value	49	2
12 months or more Gross Unrealized Losses	12	9
Total Fair Value	1,901	5,201
Total Gross Unrealized Losses	76	104
Other Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	0
Less than 12 months Gross Unrealized Losses	0	0
12 months or more Fair Value	0	0
12 months or more Gross Unrealized Losses	0	0
Total Fair Value	0	0
Total Gross Unrealized Losses	$ 0	$ 0