Note Commitments and contingencies (Commitments) - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Line Items]
Exposure Municipal Loans And Securities	74.00%
PR Government Direct Exposure
Commitments and Contingencies Disclosure [Line Items]
Concentration Risk Credit Risk Financial Instrument Maximum Exposure	$ 481,290	$ 483,580
PR Government Indirect Exposure
Commitments and Contingencies Disclosure [Line Items]
Concentration Of Risk Credit Facilities	382,000	386,000
PR Government Indirect Exposure \| PR Housing Bonds backed by second mortgage loans
Commitments and Contingencies Disclosure [Line Items]
Concentration Of Risk Credit Facilities	44,000	44,000
PR Government Indirect Exposure \| Commercial real estate
Commitments and Contingencies Disclosure [Line Items]
Concentration Of Risk Credit Facilities	25,000	25,000
PR Government Indirect Exposure \| Pass Through securities that have been economically defeased and refunded
Commitments and Contingencies Disclosure [Line Items]
Concentration Of Risk Credit Facilities	7,000	7,000
USVI Government Direct Exposure \| From USVI Government And Public Corporations
Commitments and Contingencies Disclosure [Line Items]
Concentration Risk Credit Risk Financial Instrument Maximum Exposure	80,000
Outstanding Balance \| PR Government Direct Exposure
Commitments and Contingencies Disclosure [Line Items]
Concentration Of Risk Credit Facilities	481,290	483,580
Outstanding Balance \| PR Government Indirect Exposure
Commitments and Contingencies Disclosure [Line Items]
Loans and Leases Receivable, Consumer, Mortgage with PRHA	306,000	310,000
Commitments To Extend Credit
Commitments and Contingencies Disclosure [Line Items]
Reserve of potential losses associated with unfunded loan commitments	11,000	10,000
Loans \| Outstanding Balance \| PR Government Direct Exposure
Commitments and Contingencies Disclosure [Line Items]
Concentration Of Risk Credit Facilities	434,434	434,493
Securities Investment \| Outstanding Balance \| PR Government Direct Exposure
Commitments and Contingencies Disclosure [Line Items]
Concentration Of Risk Credit Facilities	$ 46,856	$ 49,045

Commitments and Contingencies Disclosure [Line Items]

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Concentration of Risk Credit Facilities with the Puerto Rico government that is outstanding.

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The Corporations exposure to municipal loans and securities was concentrated in the municipalities of San Juan, Guaynabo, Carolina and Bayamon.

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Amount before allowance of consumer mortgage held and guaranteed by the Puerto Rico Housing Authority.

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Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

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