Commitments and contingencies - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended					9 Months Ended		1 Months Ended							9 Months Ended	12 Months Ended									3 Months Ended
	Sep. 30, 2013 D	Sep. 30, 2012	Sep. 30, 2013 D	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Minimum Member	Sep. 30, 2013 Maximum Member	Sep. 30, 2013 Parent Company [Member]	Sep. 30, 2012 Parent Company [Member]	Oct. 21, 2013 Banco Popular De Puerto Rico [Member] Arbitration With F D I C Regarding Reimbursement For Westernbank Loans [Member]	Sep. 30, 2013 Banco Popular De Puerto Rico [Member] Arbitration With F D I C Regarding Reimbursement For Westernbank Loans [Member]	Oct. 21, 2013 Credit Concentration Risk Member Outstanding Balance [Member]	Sep. 30, 2013 Credit Concentration Risk Member Outstanding Balance [Member]	Dec. 31, 2012 Credit Concentration Risk Member Outstanding Balance [Member]	Sep. 30, 2013 Credit Concentration Risk Member Foreign Government Debt Securities Member	Dec. 31, 2012 Credit Concentration Risk Member Foreign Government Debt Securities Member	Sep. 30, 2013 Credit Concentration Risk Member Commercial Real Estate Portfolio Segment Member	Dec. 31, 2012 Credit Concentration Risk Member Commercial Real Estate Portfolio Segment Member	Sep. 30, 2013 Credit Concentration Risk Member Other Credit Facilities [Member]	Dec. 31, 2012 Credit Concentration Risk Member Other Credit Facilities [Member]	Sep. 30, 2013 Credit Concentration Risk Member Uncommitted Credit Facility [Member]	Dec. 31, 2012 Credit Concentration Risk Member Uncommitted Credit Facility [Member]	Sep. 30, 2013 Credit Concentration Risk Member Uncommitted Credit Facility [Member] Outstanding Balance [Member]	Dec. 31, 2012 Credit Concentration Risk Member Uncommitted Credit Facility [Member] Outstanding Balance [Member]	Sep. 30, 2013 Commitments To Extend Credit Member	Dec. 31, 2012 Commitments To Extend Credit Member	Sep. 30, 2013 Putative Class Action [Member] Bpna [Member]
Commitments and Contingencies Disclosure [Line Items]
Reserve of potential losses associated with unfunded loan commitments																									$ 4,000,000	$ 5,000,000
Unrecorded Unconditional Purchase Obligation Balance Sheet Amount	10,000,000		10,000,000		10,000,000
Estimate of possible loss	124,000,000		124,000,000		112,000,000
Fair Value Concentration Of Risk Loans Receivable															204,000,000	217,000,000	14,200,000,000	13,300,000,000			25,000,000	75,000,000	0	61,000,000
Concentration Risk Percentage																	67.00%	64.00%
Fair Value Concentration Of Risk Credit Facilities Granted													681,000,000	681,000,000					900,000,000	800,000,000
True Up Payment Term	45		45
Loss Contingency Range Of Possible Loss Portion Not Accrued						0	15,400,000
Loss Contingency Damages Sought Value																											2,000,000
Loans and Leases Receivable, Consumer, Mortgage with PRHA												272,000,000		294,000,000
Unreimbursed Claims Late Stage Real State Collateral Dependent Loans										248,100,000
F D I C Indemnification Asset Cash Payments Received	(52,865,000)	(64,932,000)	(52,758,000)	(327,739,000)				0	0	143,100,000
Total Unreimbursed F D I C Shared Loss Claims										398,200,000	541,300,000
Methodology Computation Charge Offs										$ 123,600,000