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
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2011 Prlp2011 Holdings Llc Joint Venture [Member]	Sep. 30, 2012 Residential Mortgage	Sep. 30, 2011 Residential Mortgage	Sep. 30, 2012 Residential Mortgage	Sep. 30, 2011 Residential Mortgage	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2011 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2011 Residential Mortgage Trading Account Assets[Member]	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2011 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, 2011 Residential Mortgage Trading Account Assets[Member] Government National Mortgage Association Certificates And Obligations GNMA Member	Sep. 30, 2012 Residential Mortgage Trading Account Assets[Member] Federal National Mortgage Association Certificates And Obligations FNMA Member	Sep. 30, 2011 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, 2011 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 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, 2012 Consumer Portfolio Segment Member	Sep. 30, 2011 Consumer Portfolio Segment Member	Sep. 30, 2012 Consumer Portfolio Segment Member	Sep. 30, 2011 Consumer Portfolio Segment Member	Sep. 30, 2012 Mortgages	Sep. 30, 2011 Mortgages	Sep. 30, 2012 Mortgages	Sep. 30, 2011 Mortgages	Sep. 30, 2012 Construction Loans [Member]	Sep. 30, 2011 Construction Loans [Member]	Sep. 30, 2012 Construction Loans [Member]	Sep. 30, 2011 Construction Loans [Member]	Sep. 30, 2012 Commercial Loans [Member]	Sep. 30, 2011 Commercial Loans [Member]	Sep. 30, 2012 Commercial Loans [Member]	Sep. 30, 2011 Commercial Loans [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, 2011 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] 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, 2011 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]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable Acquired With Deteriorated Credit Quality																																								$ 300,000,000	$ 400,000,000
Outstanding principal balance of covered loans																																										5,100,000,000	6,000,000,000
Purchase of Loans																								0	130,000,000	230,000,000	130,000,000	453,000,000	177,000,000	1,100,000,000	1,100,000,000	100,000	0	1,000,000	0	0	0	0	0
Residential Mortgage Loans Sold						94,000,000	39,000,000	238,000,000	309,000,000
Commercial Construction Loans Sold	9,000,000	13,000,000	48,000,000	27,000,000	128,000,000
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds						$ 312,330,000	$ 239,924,000	$ 845,150,000	$ 844,880,000	$ 308,553,000	$ 235,810,000	$ 834,352,000	$ 829,927,000	$ 180,827,000	$ 193,731,000	$ 575,642,000	$ 666,601,000	$ 107,301,000	$ 42,079,000	$ 238,285,000	$ 163,326,000	$ 20,425,000	$ 20,425,000