Loans - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended				9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
Loans - Additional Information (Detail) (USD $)	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2013 Sale Non Performing Loans [Member]	Mar. 31, 2013 Sale Non Performing Loans [Member]	Sep. 30, 2013 Residential Mortgage	Sep. 30, 2012 Residential Mortgage	Sep. 30, 2013 Residential Mortgage	Sep. 30, 2012 Residential Mortgage	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Federal National Mortgage Association Certificates And Obligations FNMA Member	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member] Federal National Mortgage Association Certificates And Obligations FNMA Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Federal National Mortgage Association Certificates And Obligations FNMA Member	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member] Federal National Mortgage Association Certificates And Obligations FNMA Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member] Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member	Sep. 30, 2013 Residential Mortgage Trading Account Assets[Member] Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member] Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member	Sep. 30, 2013 Consumer [Member]	Sep. 30, 2012 Consumer [Member]	Sep. 30, 2013 Consumer [Member]	Sep. 30, 2012 Consumer [Member]	Sep. 30, 2013 Mortgages [Member]	Sep. 30, 2012 Mortgages [Member]	Sep. 30, 2013 Mortgages [Member]	Sep. 30, 2012 Mortgages [Member]	Sep. 30, 2013 Construction Loans [Member]	Sep. 30, 2012 Construction Loans [Member]	Sep. 30, 2013 Construction Loans [Member]	Sep. 30, 2012 Construction Loans [Member]	Sep. 30, 2013 Commercial Loans [Member]	Sep. 30, 2012 Commercial Loans [Member]	Sep. 30, 2013 Commercial Loans [Member]	Sep. 30, 2012 Commercial Loans [Member]	Sep. 30, 2013 Westernbank Puerto Rico [Member] A S C Subtopic 31020 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]	Sep. 30, 2012 Westernbank Puerto Rico [Member] A S C Subtopic 31020 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]	Sep. 30, 2013 Westernbank Puerto Rico [Member] Covered Under Loss Sharing Agreements With F D I C [Member] A S C Subtopic 31030 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]	Dec. 31, 2012 Westernbank Puerto Rico [Member] Covered Under Loss Sharing Agreements With F D I C [Member] A S C Subtopic 31030 [Member] Acquired Loans In An F D I C Assisted Transaction [Member]	Sep. 30, 2013 SOP Non-Covered Loans [Member] A S C Subtopic 31030 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable Acquired With Deteriorated Credit Quality																																											$ 200,000,000	$ 300,000,000
Outstanding principal balance of covered loans																																													3,900,000,000	4,800,000,000	175,000,000
Purchase of Loans																											0	230,000,000	42,000,000	230,000,000	199,000,000	453,000,000	1,700,000,000	1,100,000,000	0	100,000	0	1,000,000	5,000,000	0	8,000,000	0
Residential Mortgage Loans Sold					435,000,000		60,000,000	94,000,000	614,000,000	238,000,000
Commercial Construction Loans Sold	6,000	9,000	413,000	48,000		401,000,000
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds							$ 307,339,000	$ 312,330,000	$ 1,163,045,000	$ 845,150,000	$ 302,873,000	$ 308,553,000	$ 1,149,199,000	$ 834,352,000	$ 199,824,000	$ 180,827,000	$ 767,393,000	$ 575,642,000	$ 101,922,000	$ 107,301,000	$ 353,987,000	$ 238,285,000	$ 1,127,000	$ 20,425,000	$ 27,819,000	$ 20,425,000

The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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