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	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 4,915,752	$ 4,779,077	$ 5,521,745
Gross Unrealized Gains	227,545	238,461	174,126
Gross Unrealized Losses	4,681	7,715	9,530
Fair Value	5,138,616	5,009,823	5,686,341
Weighted Average Yield	3.40%	3.58%	3.67%
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	34,802	34,980	35,508
Gross Unrealized Gains	3,282	3,688	2,174
Gross Unrealized Losses	0	0	0
Fair Value	38,084	38,668	37,682
Weighted Average Yield	3.35%	3.35%	3.35%
US Treasury Securities [Member] | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,012	0	0
Gross Unrealized Gains	84	0	0
Gross Unrealized Losses	0	0	0
Fair Value	7,096	0	0
Weighted Average Yield	1.50%	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	27,790	34,980	7,003
Gross Unrealized Gains	3,198	3,688	98
Gross Unrealized Losses	0	0	0
Fair Value	30,988	38,668	7,101
Weighted Average Yield	3.82%	3.35%	1.50%
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	28,505
Gross Unrealized Gains	0	0	2,076
Gross Unrealized Losses	0	0	0
Fair Value	0	0	30,581
Weighted Average Yield	0.00%	0.00%	3.81%
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	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Fair Value	0	0	0
Weighted Average Yield	0.00%	0.00%	0.00%
US Government Sponsored Enterprises Debt Securities Member
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,066,834	953,836	1,416,027
Gross Unrealized Gains	26,291	31,710	46,591
Gross Unrealized Losses	1,327	0	1,531
Fair Value	1,091,798	985,546	1,461,087
Weighted Average Yield	3.00%	3.30%	3.47%
US Government Sponsored Enterprises Debt Securities Member | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,515	94,492	230,290
Gross Unrealized Gains	1,735	2,382	906
Gross Unrealized Losses	0	0	921
Fair Value	101,250	96,874	230,275
Weighted Average Yield	3.36%	3.45%	2.95%
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	625,230	655,625	1,005,737
Gross Unrealized Gains	21,897	25,860	45,685
Gross Unrealized Losses	0	0	92
Fair Value	647,127	681,485	1,051,330
Weighted Average Yield	3.31%	3.38%	3.73%
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	310,004	171,633	180,000
Gross Unrealized Gains	2,290	2,969	0
Gross Unrealized Losses	940	0	518
Fair Value	311,354	174,602	179,482
Weighted Average Yield	2.14%	2.94%	2.66%
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	32,085	32,086	0
Gross Unrealized Gains	369	499	0
Gross Unrealized Losses	387	0	0
Fair Value	32,067	32,585	0
Weighted Average Yield	4.00%	3.20%	0.00%
Obligations of Puerto Rico, States and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	55,719	57,504	52,380
Gross Unrealized Gains	1,140	1,255	362
Gross Unrealized Losses	23	31	173
Fair Value	56,836	58,728	52,569
Weighted Average Yield	5.06%	5.03%	4.70%
Obligations of Puerto Rico, States and political subdivisions | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	765	765	10,357
Gross Unrealized Gains	4	9	10
Gross Unrealized Losses	0	0	0
Fair Value	769	774	10,367
Weighted Average Yield	4.94%	4.97%	3.92%
Obligations of Puerto Rico, States and political subdivisions | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,039	14,824	15,753
Gross Unrealized Gains	296	283	255
Gross Unrealized Losses	23	31	6
Fair Value	13,312	15,076	16,002
Weighted Average Yield	4.04%	4.07%	4.52%
Obligations of Puerto Rico, States and political subdivisions | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,595	4,595	20,765
Gross Unrealized Gains	41	54	35
Gross Unrealized Losses	0	0	167
Fair Value	4,636	4,649	20,633
Weighted Average Yield	5.33%	5.33%	5.07%
Obligations of Puerto Rico, States and political subdivisions | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	37,320	37,320	5,505
Gross Unrealized Gains	799	909	62
Gross Unrealized Losses	0	0	0
Fair Value	38,119	38,229	5,567
Weighted Average Yield	5.38%	5.38%	5.28%
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	1,805,782	1,646,893	1,580,113
Gross Unrealized Gains	53,419	50,957	29,108
Gross Unrealized Losses	394	208	1,876
Fair Value	1,858,807	1,697,642	1,607,345
Weighted Average Yield	2.66%	2.83%	2.91%
Collateralized Mortgage Obligations Issued By U S Government Sponsored Enterprises And U S Government [Member] | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0	35
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Fair Value	0	0	35
Weighted Average Yield	0.00%	0.00%	3.36%
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	6,822	2,424	1,737
Gross Unrealized Gains	81	49	88
Gross Unrealized Losses	0	0	0
Fair Value	6,903	2,473	1,825
Weighted Average Yield	1.48%	3.28%	4.76%
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	41,988	55,096	91,067
Gross Unrealized Gains	1,347	1,446	1,019
Gross Unrealized Losses	0	0	865
Fair Value	43,335	56,542	91,221
Weighted Average Yield	2.86%	2.64%	2.47%
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	1,756,972	1,589,373	1,487,274
Gross Unrealized Gains	51,991	49,462	28,001
Gross Unrealized Losses	394	208	1,011
Fair Value	1,808,569	1,638,627	1,514,264
Weighted Average Yield	2.66%	2.84%	2.94%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	57,486	65,113	81,721
Gross Unrealized Gains	71	1	64
Gross Unrealized Losses	2,889	7,322	4,637
Fair Value	54,668	57,792	77,148
Weighted Average Yield	2.37%	2.30%	2.16%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member] | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Fair Value	0	0	0
Weighted Average Yield	0.00%	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	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Fair Value	0	0	0
Weighted Average Yield	0.00%	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	5,041	5,653	8,109
Gross Unrealized Gains	1	1	13
Gross Unrealized Losses	149	181	90
Fair Value	4,893	5,473	8,032
Weighted Average Yield	0.77%	0.81%	0.86%
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	52,445	59,460	73,612
Gross Unrealized Gains	70	0	51
Gross Unrealized Losses	2,740	7,141	4,547
Fair Value	49,775	52,319	69,116
Weighted Average Yield	2.52%	2.44%	2.30%
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,865,274	1,989,996	2,321,951
Gross Unrealized Gains	139,287	149,623	92,496
Gross Unrealized Losses	37	50	979
Fair Value	2,004,524	2,139,569	2,413,468
Weighted Average Yield	4.26%	4.27%	4.28%
Collateralized Mortgage Backed Securities [Member] | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32	57	633
Gross Unrealized Gains	0	1	51
Gross Unrealized Losses	0	0	0
Fair Value	32	58	684
Weighted Average Yield	3.71%	3.91%	5.35%
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	6,619	7,564	13,444
Gross Unrealized Gains	311	328	519
Gross Unrealized Losses	0	0	4
Fair Value	6,930	7,892	13,959
Weighted Average Yield	3.90%	3.86%	3.98%
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	102,677	111,639	164,579
Gross Unrealized Gains	7,837	8,020	10,230
Gross Unrealized Losses	1	1	8
Fair Value	110,513	119,658	174,801
Weighted Average Yield	4.67%	4.66%	4.71%
Collateralized Mortgage Backed Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,755,946	1,870,736	2,143,295
Gross Unrealized Gains	131,139	141,274	81,696
Gross Unrealized Losses	36	49	967
Fair Value	1,887,049	2,011,961	2,224,024
Weighted Average Yield	4.24%	4.25%	4.25%
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,595	6,594	8,722
Gross Unrealized Gains	875	426	968
Gross Unrealized Losses	11	104	256
Fair Value	7,459	6,916	9,434
Weighted Average Yield	2.81%	2.96%	3.43%
Other
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,260	24,161	25,323
Gross Unrealized Gains	3,180	801	2,363
Gross Unrealized Losses	0	0	78
Fair Value	26,440	24,962	27,608
Weighted Average Yield	9.28%	9.06%	8.82%
Other | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Fair Value	0	0	0
Weighted Average Yield	0.00%	0.00%	0.00%
Other | More Than One And Within Five Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	0	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Fair Value	0	0	0
Weighted Average Yield	0.00%	0.00%	0.00%
Other | More Than Five And Within Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,850	17,850	17,850
Gross Unrealized Gains	3,063	700	2,363
Gross Unrealized Losses	0	0	0
Fair Value	20,913	18,550	20,213
Weighted Average Yield	10.99%	10.99%	11.00%
Other | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,410	6,311	7,473
Gross Unrealized Gains	117	101	0
Gross Unrealized Losses	0	0	78
Fair Value	$ 5,527	$ 6,412	$ 7,395
Weighted Average Yield	3.62%	3.61%	3.62%