Amortized cost, gross unrealized gains and losses, approximate fair value, weighted average yield and contractual maturities of investment securities available-for-sale (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 5,505,395	$ 5,307,250
Gross Unrealized Gains	87,435	73,411
Gross Unrealized Losses	44,127	65,502
Investment securities available-for-sale, at fair value	5,548,703	5,315,159
Weighted Average Yield	2.08%	2.04%
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	777,468	698,003
Gross Unrealized Gains	6,806	2,226
Gross Unrealized Losses	0	75
Investment securities available-for-sale, at fair value	784,274	700,154
Weighted Average Yield	1.12%	1.14%
US Treasury Securities [Member] | Within One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
US Treasury Securities [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	777,468	698,003
Gross Unrealized Gains	6,806	2,226
Gross Unrealized Losses	0	75
Investment securities available-for-sale, at fair value	784,274	700,154
Weighted Average Yield	1.12%	1.14%
US Treasury Securities [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
US Treasury Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
US Government Sponsored Enterprises Debt Securities Member
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,500,783	1,735,758
Gross Unrealized Gains	4,337	1,606
Gross Unrealized Losses	2,986	12,391
Investment securities available-for-sale, at fair value	1,502,134	1,724,973
Weighted Average Yield	1.31%	1.31%
US Government Sponsored Enterprises Debt Securities Member | Within One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	35,160	42,140
Gross Unrealized Gains	254	380
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	35,414	42,520
Weighted Average Yield	1.87%	1.61%
US Government Sponsored Enterprises Debt Securities Member | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,412,508	1,603,245
Gross Unrealized Gains	3,965	1,168
Gross Unrealized Losses	2,168	9,936
Investment securities available-for-sale, at fair value	1,414,305	1,594,477
Weighted Average Yield	1.25%	1.26%
US Government Sponsored Enterprises Debt Securities Member | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,115	67,373
Gross Unrealized Gains	52	58
Gross Unrealized Losses	818	2,271
Investment securities available-for-sale, at fair value	29,349	65,160
Weighted Average Yield	1.98%	1.72%
US Government Sponsored Enterprises Debt Securities Member | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,000	23,000
Gross Unrealized Gains	66	0
Gross Unrealized Losses	0	184
Investment securities available-for-sale, at fair value	23,066	22,816
Weighted Average Yield	3.19%	3.18%
Puerto Rico States And Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	75,299	75,164
Gross Unrealized Gains	2	97
Gross Unrealized Losses	17,937	13,549
Investment securities available-for-sale, at fair value	57,364	61,712
Weighted Average Yield	6.04%	6.04%
Puerto Rico States And Political Subdivisions Debt Securities [Member] | Within One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,758	2,765
Gross Unrealized Gains	0	17
Gross Unrealized Losses	1	0
Investment securities available-for-sale, at fair value	2,757	2,782
Weighted Average Yield	3.83%	3.83%
Puerto Rico States And Political Subdivisions Debt Securities [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,036	1,024
Gross Unrealized Gains	0	38
Gross Unrealized Losses	189	0
Investment securities available-for-sale, at fair value	6,847	1,062
Weighted Average Yield	4.10%	8.40%
Puerto Rico States And Political Subdivisions Debt Securities [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,662	22,552
Gross Unrealized Gains	0	2
Gross Unrealized Losses	3,075	2,331
Investment securities available-for-sale, at fair value	13,587	20,223
Weighted Average Yield	6.68%	5.82%
Puerto Rico States And Political Subdivisions Debt Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,843	48,823
Gross Unrealized Gains	2	40
Gross Unrealized Losses	14,672	11,218
Investment securities available-for-sale, at fair value	34,173	37,645
Weighted Average Yield	6.22%	6.22%
Collateralized Mortgage Obligations Issued By U S Government Sponsored Enterprises And U S Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,854,226	1,934,652
Gross Unrealized Gains	16,598	14,181
Gross Unrealized Losses	21,798	38,803
Investment securities available-for-sale, at fair value	1,849,026	1,910,030
Weighted Average Yield	2.03%	2.04%
Collateralized Mortgage Obligations Issued By U S Government Sponsored Enterprises And U S Government [Member] | Within One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Obligations Issued By U S Government Sponsored Enterprises And U S Government [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,943	3,687
Gross Unrealized Gains	889	87
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	19,832	3,774
Weighted Average Yield	2.95%	2.66%
Collateralized Mortgage Obligations Issued By U S Government Sponsored Enterprises And U S Government [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	52,779	25,202
Gross Unrealized Gains	1,269	985
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	54,048	26,187
Weighted Average Yield	2.72%	2.93%
Collateralized Mortgage Obligations Issued By U S Government Sponsored Enterprises And U S Government [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,782,504	1,905,763
Gross Unrealized Gains	14,440	13,109
Gross Unrealized Losses	21,798	38,803
Investment securities available-for-sale, at fair value	1,775,146	1,880,069
Weighted Average Yield	2.01%	2.03%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member] | Within One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,285,424	851,088
Gross Unrealized Gains	58,352	53,958
Gross Unrealized Losses	1,403	684
Investment securities available-for-sale, at fair value	1,342,373	904,362
Weighted Average Yield	3.41%	3.88%
Collateralized Mortgage Backed Securities [Member] | Within One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
Collateralized Mortgage Backed Securities [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,869	27,339
Gross Unrealized Gains	1,318	1,597
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	26,187	28,936
Weighted Average Yield	4.68%	4.68%
Collateralized Mortgage Backed Securities [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	140,493	147,182
Gross Unrealized Gains	7,319	7,314
Gross Unrealized Losses	3	1
Investment securities available-for-sale, at fair value	147,809	154,495
Weighted Average Yield	3.51%	3.51%
Collateralized Mortgage Backed Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,120,062	676,567
Gross Unrealized Gains	49,715	45,047
Gross Unrealized Losses	1,400	683
Investment securities available-for-sale, at fair value	1,168,377	720,931
Weighted Average Yield	3.37%	3.93%
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,350	1,351
Gross Unrealized Gains	1,284	1,271
Gross Unrealized Losses	3	0
Investment securities available-for-sale, at fair value	2,631	2,622
Weighted Average Yield	1.37%	5.03%
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,845	11,234
Gross Unrealized Gains	56	72
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	10,901	11,306
Weighted Average Yield	1.99%	2.03%
Other Securities [Member] | Within One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	0	0
Weighted Average Yield	0.00%	0.00%
Other Securities [Member] | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,187	9,277
Gross Unrealized Gains	12	10
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	9,199	9,287
Weighted Average Yield	1.69%	1.69%
Other Securities [Member] | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,658	1,957
Gross Unrealized Gains	44	62
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	1,702	2,019
Weighted Average Yield	3.62%	3.63%
Other Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Investment securities available-for-sale, at fair value	$ 0	$ 0
Weighted Average Yield	0.00%	0.00%