Pension plans and other postretirement benefits - Defined Benefit Plan Estimated Future Benefit Payments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Pension benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
2013	$ 62,531
2014	66,096
2015	68,838
2016	75,769
2017	78,564
2018 through 2022	450,434
Other postretirement benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
2013	7,473
2014	7,151
2015	6,883
2016	6,652
2017	6,332
2018 through 2022	$ 27,647

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Amount of benefits expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

+ Details

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- Definition

Amount of benefits expected to be paid in the next fiscal year following the latest fiscal year from a defined benefit plan.

+ References

+ Details

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- Definition

Amount of benefits expected to be paid in the fifth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

+ Details

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- Definition

Amount of benefits expected to be paid in the fourth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

+ Details

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- Definition

Amount of benefits expected to be paid in the third fiscal year following the latest fiscal year from a defined benefit plan.

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- Definition

Amount of benefits expected to be paid in the second fiscal year following the latest fiscal year from a defined benefit plan.

+ References

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