Pension and Other Postretirement Benefits - Summary of Pension Plan Benefit to Participants (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2013	$ 31,376
2014	28,527
2015	28,572
2016	28,650
2017	28,568
Next 5 years	142,233
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
2013	1,194
2014	3,996
2015	3,933
2016	3,863
2017	3,789
Next 5 years	$ 17,673

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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

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

+ References

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

+ References

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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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