Pension and Other Postretirement Benefits - Effect of One Percentage - Point Change in Assumed Health Care Cost Trend Rates (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Postemployment Benefits [Abstract]
Effect on total of service and interest cost components, 1% Increase	$ 142
Effect on postretirement benefit obligation, 1% Increase	3,629
Effect on total of service and interest cost components, 1% Decrease	(118)
Effect on postretirement benefit obligation, 1% Decrease	$ (3,006)

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (m)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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- Definition

Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

+ References

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- Definition

The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

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