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	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 4,922,292	$ 4,779,077
Gross Unrealized Gains	200,761	238,461
Gross Unrealized Losses	2,752	7,715
Fair Value	5,120,301	5,009,823
Weighted Average Yield	3.14%	3.58%
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	34,439	34,980
Gross Unrealized Gains	3,268	3,688
Gross Unrealized Losses	0	0
Fair Value	37,707	38,668
Weighted Average Yield	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	7,016	0
Gross Unrealized Gains	43	0
Gross Unrealized Losses	0	0
Fair Value	7,059	0
Weighted Average Yield	1.50%	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	27,423	34,980
Gross Unrealized Gains	3,225	3,688
Gross Unrealized Losses	0	0
Fair Value	30,648	38,668
Weighted Average Yield	3.82%	3.35%
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
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
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	1,047,064	953,836
Gross Unrealized Gains	18,075	31,710
Gross Unrealized Losses	172	0
Fair Value	1,064,967	985,546
Weighted Average Yield	2.89%	3.30%
US Government Sponsored Enterprises Debt Securities Member | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	539,000	94,492
Gross Unrealized Gains	11,603	2,382
Gross Unrealized Losses	0	0
Fair Value	550,603	96,874
Weighted Average Yield	3.93%	3.45%
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	190,521	655,625
Gross Unrealized Gains	2,661	25,860
Gross Unrealized Losses	0	0
Fair Value	193,182	681,485
Weighted Average Yield	1.57%	3.38%
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	317,543	171,633
Gross Unrealized Gains	3,811	2,969
Gross Unrealized Losses	172	0
Fair Value	321,182	174,602
Weighted Average Yield	1.93%	2.94%
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	0	32,086
Gross Unrealized Gains	0	499
Gross Unrealized Losses	0	0
Fair Value	0	32,585
Weighted Average Yield	0.00%	3.20%
Puerto Rico States And Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,772	57,504
Gross Unrealized Gains	1,274	1,255
Gross Unrealized Losses	42	31
Fair Value	50,004	58,728
Weighted Average Yield	5.27%	5.03%
Puerto Rico States And Political Subdivisions Debt Securities [Member] | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,220	765
Gross Unrealized Gains	43	9
Gross Unrealized Losses	0	0
Fair Value	5,263	774
Weighted Average Yield	5.26%	4.97%
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	6,262	14,824
Gross Unrealized Gains	169	283
Gross Unrealized Losses	42	31
Fair Value	6,389	15,076
Weighted Average Yield	4.65%	4.07%
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	0	4,595
Gross Unrealized Gains	0	54
Gross Unrealized Losses	0	0
Fair Value	0	4,649
Weighted Average Yield	0.00%	5.33%
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	37,290	37,320
Gross Unrealized Gains	1,062	909
Gross Unrealized Losses	0	0
Fair Value	38,352	38,229
Weighted Average Yield	5.38%	5.38%
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	2,167,916	1,646,893
Gross Unrealized Gains	50,442	50,957
Gross Unrealized Losses	1,316	208
Fair Value	2,217,042	1,697,642
Weighted Average Yield	2.36%	2.83%
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
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
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	5,506	2,424
Gross Unrealized Gains	51	49
Gross Unrealized Losses	0	0
Fair Value	5,557	2,473
Weighted Average Yield	1.49%	3.28%
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	45,831	55,096
Gross Unrealized Gains	2,067	1,446
Gross Unrealized Losses	0	0
Fair Value	47,898	56,542
Weighted Average Yield	2.96%	2.64%
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	2,116,579	1,589,373
Gross Unrealized Gains	48,324	49,462
Gross Unrealized Losses	1,316	208
Fair Value	2,163,587	1,638,627
Weighted Average Yield	2.35%	2.84%
Collateralized Mortgage Obligations Issued By Private Enterprise [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	39,789	65,113
Gross Unrealized Gains	230	1
Gross Unrealized Losses	1,106	7,322
Fair Value	38,913	57,792
Weighted Average Yield	2.66%	2.30%
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
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
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
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	35	5,653
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	181
Fair Value	36	5,473
Weighted Average Yield	4.88%	0.81%
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	39,754	59,460
Gross Unrealized Gains	229	0
Gross Unrealized Losses	1,106	7,141
Fair Value	38,877	52,319
Weighted Average Yield	2.66%	2.44%
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,555,343	1,989,996
Gross Unrealized Gains	123,957	149,623
Gross Unrealized Losses	40	50
Fair Value	1,679,260	2,139,569
Weighted Average Yield	4.24%	4.27%
Collateralized Mortgage Backed Securities [Member] | One Year From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	600	57
Gross Unrealized Gains	24	1
Gross Unrealized Losses	0	0
Fair Value	624	58
Weighted Average Yield	3.80%	3.91%
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	3,705	7,564
Gross Unrealized Gains	196	328
Gross Unrealized Losses	0	0
Fair Value	3,901	7,892
Weighted Average Yield	3.94%	3.86%
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	89,364	111,639
Gross Unrealized Gains	7,258	8,020
Gross Unrealized Losses	0	1
Fair Value	96,622	119,658
Weighted Average Yield	4.71%	4.66%
Collateralized Mortgage Backed Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,461,674	1,870,736
Gross Unrealized Gains	116,479	141,274
Gross Unrealized Losses	40	49
Fair Value	1,578,113	2,011,961
Weighted Average Yield	4.21%	4.25%
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,595	6,594
Gross Unrealized Gains	1,011	426
Gross Unrealized Losses	76	104
Fair Value	7,530	6,916
Weighted Average Yield	3.41%	2.96%
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,374	24,161
Gross Unrealized Gains	2,504	801
Gross Unrealized Losses	0	0
Fair Value	24,878	24,962
Weighted Average Yield	9.57%	9.06%
Other Securities [Member] | 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
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	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
Weighted Average Yield	0.00%	0.00%
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	18,032	17,850
Gross Unrealized Gains	2,363	700
Gross Unrealized Losses	0	0
Fair Value	20,395	18,550
Weighted Average Yield	11.00%	10.99%
Other Securities [Member] | More Than Ten Years From Balance Sheet Date [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,342	6,311
Gross Unrealized Gains	141	101
Gross Unrealized Losses	0	0
Fair Value	$ 4,483	$ 6,412
Weighted Average Yield	3.61%	3.61%