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	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 2,223,735	$ 3,055,888
Less than 12 months Gross Unrealized Losses	38,567	119,453
12 months or more Fair Value	1,310,546	190,985
12 months or more Gross Unrealized Losses	54,623	10,981
Total Fair Value	3,534,281	3,246,873
Total Gross Unrealized Losses	93,190	130,434
US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	315,946
Less than 12 months Gross Unrealized Losses	685
12 months or more Fair Value	0
12 months or more Gross Unrealized Losses	0
Total Fair Value	315,946
Total Gross Unrealized Losses	685
US Government Sponsored Enterprises Debt Securities Member
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	1,103,884	1,326,866
Less than 12 months Gross Unrealized Losses	10,762	32,457
12 months or more Fair Value	466,218	69,257
12 months or more Gross Unrealized Losses	9,150	4,240
Total Fair Value	1,570,102	1,396,123
Total Gross Unrealized Losses	19,912	36,697
Puerto Rico States And Political Subdivisions Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	25,773	54,256
Less than 12 months Gross Unrealized Losses	2,254	11,685
12 months or more Fair Value	35,107	8,330
12 months or more Gross Unrealized Losses	8,558	190
Total Fair Value	60,880	62,586
Total Gross Unrealized Losses	10,812	11,875
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	767,902	1,567,654
Less than 12 months Gross Unrealized Losses	24,824	70,378
12 months or more Fair Value	748,428	96,676
12 months or more Gross Unrealized Losses	34,514	5,645
Total Fair Value	1,516,330	1,664,330
Total Gross Unrealized Losses	59,338	76,023
Collateralized Mortgage Obligations Issued By Private Enterprise [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
Collateralized Mortgage Backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	10,230	105,455
Less than 12 months Gross Unrealized Losses	42	4,762
12 months or more Fair Value	49,805	7,225
12 months or more Gross Unrealized Losses	2,193	765
Total Fair Value	60,035	112,680
Total Gross Unrealized Losses	2,235	5,527
Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	1,657
Less than 12 months Gross Unrealized Losses	0	171
12 months or more Fair Value	1,671	0
12 months or more Gross Unrealized Losses	157	0
Total Fair Value	1,671	1,657
Total Gross Unrealized Losses	157	171
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	9,317	9,497
12 months or more Gross Unrealized Losses	51	141
Total Fair Value	9,317	9,497
Total Gross Unrealized Losses	$ 51	$ 141