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	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 1,603,031	$ 1,492,324
Less than 12 months Gross Unrealized Losses	19,901	23,750
12 months or more Fair Value	1,212,251	1,230,219
12 months or more Gross Unrealized Losses	35,484	41,752
Total Fair Value	2,815,282	2,722,543
Total Gross Unrealized Losses	55,385	65,502
US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	39,918	49,465
Less than 12 months Gross Unrealized Losses	58	75
12 months or more Fair Value	0	0
12 months or more Gross Unrealized Losses	0	0
Total Fair Value	39,918	49,465
Total Gross Unrealized Losses	58	75
US Government Sponsored Enterprises Debt Securities Member
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	372,506	888,325
Less than 12 months Gross Unrealized Losses	1,723	6,866
12 months or more Fair Value	271,839	429,835
12 months or more Gross Unrealized Losses	2,968	5,525
Total Fair Value	644,345	1,318,160
Total Gross Unrealized Losses	4,691	12,391
Puerto Rico States And Political Subdivisions Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	15,820	14,419
Less than 12 months Gross Unrealized Losses	6,528	3,031
12 months or more Fair Value	8,735	41,084
12 months or more Gross Unrealized Losses	2,328	10,518
Total Fair Value	24,555	55,503
Total Gross Unrealized Losses	8,856	13,549
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	303,544	539,658
Less than 12 months Gross Unrealized Losses	3,252	13,774
12 months or more Fair Value	907,897	733,814
12 months or more Gross Unrealized Losses	29,267	25,029
Total Fair Value	1,211,441	1,273,472
Total Gross Unrealized Losses	32,519	38,803
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	862,115	457
Less than 12 months Gross Unrealized Losses	8,323	4
12 months or more Fair Value	23,780	25,486
12 months or more Gross Unrealized Losses	921	680
Total Fair Value	885,895	25,943
Total Gross Unrealized Losses	9,244	684
Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	47	0
Less than 12 months Gross Unrealized Losses	3	0
12 months or more Fair Value	0	0
12 months or more Gross Unrealized Losses	0	0
Total Fair Value	47	0
Total Gross Unrealized Losses	3	0
Other Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	9,081	0
Less than 12 months Gross Unrealized Losses	14	0
12 months or more Fair Value	0	0
12 months or more Gross Unrealized Losses	0	0
Total Fair Value	9,081	0
Total Gross Unrealized Losses	$ 14	$ 0