Note Investment Securities Available for Sale (Amortized cost, gross unrealized gains and losses, approximate fair value, weighted average yield and contractual maturities of investment securities AFS) (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016		Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,583,611	[1]	$ 6,073,005	[2]
Gross Unrealized Gains	87,096		53,350
Gross Unrealized Losses	20,877		63,363
Investment securities available-for-sale, at fair value	$ 6,649,830	[1]	$ 6,062,992	[2]
Weighted Average Yield	2.07%		2.07%
US Treasury Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,316,085		$ 1,184,605
Gross Unrealized Gains	7,267		722
Gross Unrealized Losses	0		1,999
Investment securities available-for-sale, at fair value	$ 1,323,352		$ 1,183,328
Weighted Average Yield	1.11%		1.11%
US Treasury Securities | Within 1 year
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 24,665		$ 24,861
Gross Unrealized Gains	143		335
Gross Unrealized Losses	0		0
Investment securities available-for-sale, at fair value	$ 24,808		$ 25,196
Weighted Average Yield	4.92%		4.31%
US Treasury Securities | After 1 and within 5 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,281,481		$ 1,149,807
Gross Unrealized Gains	6,792		365
Gross Unrealized Losses	0		1,999
Investment securities available-for-sale, at fair value	$ 1,288,273		$ 1,148,173
Weighted Average Yield	1.03%		1.03%
US Treasury Securities | After 5 to 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 9,939		$ 9,937
Gross Unrealized Gains	332		22
Gross Unrealized Losses	0		0
Investment securities available-for-sale, at fair value	$ 10,271		$ 9,959
Weighted Average Yield	1.99%		1.99%
Obligations of U.S. Government sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 927,881		$ 943,069
Gross Unrealized Gains	5,224		1,380
Gross Unrealized Losses	167		4,808
Investment securities available-for-sale, at fair value	$ 932,938		$ 939,641
Weighted Average Yield	1.38%		1.38%
Obligations of U.S. Government sponsored entities | After 1 and within 5 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 904,631		$ 919,819
Gross Unrealized Gains	5,221		1,337
Gross Unrealized Losses	109		4,808
Investment securities available-for-sale, at fair value	$ 909,743		$ 916,348
Weighted Average Yield	1.33%		1.33%
Obligations of U.S. Government sponsored entities | After 5 to 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 250		$ 250
Gross Unrealized Gains	3		1
Gross Unrealized Losses	0		0
Investment securities available-for-sale, at fair value	$ 253		$ 251
Weighted Average Yield	5.64%		5.64%
Obligations of U.S. Government sponsored entities | After 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 23,000		$ 23,000
Gross Unrealized Gains	0		42
Gross Unrealized Losses	58		0
Investment securities available-for-sale, at fair value	$ 22,942		$ 23,042
Weighted Average Yield	3.24%		3.22%
Obligations of Puerto Rico, States and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 31,821		$ 31,737
Gross Unrealized Gains	2		0
Gross Unrealized Losses	8,093		9,378
Investment securities available-for-sale, at fair value	$ 23,730		$ 22,359
Weighted Average Yield	5.72%		5.74%
Obligations of Puerto Rico, States and political subdivisions | After 1 and within 5 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 7,292		$ 7,227
Gross Unrealized Gains	0		0
Gross Unrealized Losses	176		199
Investment securities available-for-sale, at fair value	$ 7,116		$ 7,028
Weighted Average Yield	3.88%		3.94%
Obligations of Puerto Rico, States and political subdivisions | After 5 to 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 5,925		$ 5,925
Gross Unrealized Gains	1		0
Gross Unrealized Losses	1,963		2,200
Investment securities available-for-sale, at fair value	$ 3,963		$ 3,725
Weighted Average Yield	4.02%		4.02%
Obligations of Puerto Rico, States and political subdivisions | After 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 18,604		$ 18,585
Gross Unrealized Gains	1		0
Gross Unrealized Losses	5,954		6,979
Investment securities available-for-sale, at fair value	$ 12,651		$ 11,606
Weighted Average Yield	6.99%		6.99%
Collateralized Mortgage Obligations - Federal agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,509,133		$ 1,584,693
Gross Unrealized Gains	15,763		9,464
Gross Unrealized Losses	11,325		33,320
Investment securities available-for-sale, at fair value	$ 1,513,571		$ 1,560,837
Weighted Average Yield	2.01%		2.02%
Collateralized Mortgage Obligations - Federal agencies | Within 1 year
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 282
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Investment securities available-for-sale, at fair value	$ 282
Weighted Average Yield	0.95%
Collateralized Mortgage Obligations - Federal agencies | After 1 and within 5 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 20,257		$ 21,446
Gross Unrealized Gains	918		594
Gross Unrealized Losses	0		37
Investment securities available-for-sale, at fair value	$ 21,175		$ 22,003
Weighted Average Yield	2.86%		2.81%
Collateralized Mortgage Obligations - Federal agencies | After 5 to 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 41,078		$ 44,585
Gross Unrealized Gains	818		733
Gross Unrealized Losses	0		0
Investment securities available-for-sale, at fair value	$ 41,896		$ 45,318
Weighted Average Yield	2.86%		2.85%
Collateralized Mortgage Obligations - Federal agencies | After 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,447,516		$ 1,518,662
Gross Unrealized Gains	14,027		8,137
Gross Unrealized Losses	11,325		33,283
Investment securities available-for-sale, at fair value	$ 1,450,218		$ 1,493,516
Weighted Average Yield	1.98%		1.99%
Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,787,301		$ 2,317,329
Gross Unrealized Gains	57,695		40,692
Gross Unrealized Losses	1,290		13,825
Investment securities available-for-sale, at fair value	$ 2,843,706		$ 2,344,196
Weighted Average Yield	2.74%		2.81%
Mortgage Backed Securities | Within 1 year
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 25
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Investment securities available-for-sale, at fair value	$ 25
Weighted Average Yield	4.80%
Mortgage Backed Securities | After 1 and within 5 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 20,808		$ 22,015
Gross Unrealized Gains	990		987
Gross Unrealized Losses	6		8
Investment securities available-for-sale, at fair value	$ 21,792		$ 22,994
Weighted Average Yield	4.64%		4.65%
Mortgage Backed Securities | After 5 to 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 281,359		$ 256,097
Gross Unrealized Gains	6,195		4,866
Gross Unrealized Losses	2		1,197
Investment securities available-for-sale, at fair value	$ 287,552		$ 259,766
Weighted Average Yield	2.43%		2.51%
Mortgage Backed Securities | After 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,485,109		$ 2,039,217
Gross Unrealized Gains	50,510		34,839
Gross Unrealized Losses	1,282		12,620
Investment securities available-for-sale, at fair value	$ 2,534,337		$ 2,061,436
Weighted Average Yield	2.76%		2.83%
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,351		$ 1,350
Gross Unrealized Gains	1,090		1,053
Gross Unrealized Losses	2		5
Investment securities available-for-sale, at fair value	$ 2,439		$ 2,398
Weighted Average Yield	7.82%		7.92%
Other
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 10,039		$ 10,222
Gross Unrealized Gains	55		39
Gross Unrealized Losses	0		28
Investment securities available-for-sale, at fair value	$ 10,094		$ 10,233
Weighted Average Yield	1.95%		1.95%
Other | After 1 and within 5 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 8,819		$ 8,911
Gross Unrealized Gains	10		0
Gross Unrealized Losses	0		28
Investment securities available-for-sale, at fair value	$ 8,829		$ 8,883
Weighted Average Yield	1.72%		1.71%
Other | After 5 to 10 years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,220		$ 1,311
Gross Unrealized Gains	45		39
Gross Unrealized Losses	0		0
Investment securities available-for-sale, at fair value	$ 1,265		$ 1,350
Weighted Average Yield	3.62%		3.62%

[1] Includes $2.2 billion pledged to secure public and trust deposits, assets sold under agreements to repurchase, credit facilities and loan servicing agreements that the secured parties are not permitted to sell or repledge the collateral, of which $1.3 billion serve as collateral for public funds.

[2] Includes $2.4 billion pledged to secure public and trust deposits, assets sold under agreements to repurchase, credit facilities and loan servicing agreements that the secured parties are not permitted to sell or repledge the collateral, of which $1.5 billion serve as collateral for public funds.