Retirement Plans - Schedule of Weighted-Average Assumptions Used to Determine Net Periodic Cost (Detail) (Net Periodic Cost [Member])	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Periodic Cost [Member]
Net Periodic Benefit Cost Assumptions [Line Items]
Discount rate	4.01%	3.31%	4.22%
Health care cost trend: Initial	6.75%	7.00%	8.00%
Health care cost trend: Ultimate	4.75%	4.75%	4.75%
Year ultimate reached	2022	2022	2016
Corridor	10.00%	10.00%	10.00%
Recognition period for gains and losses	10 years	11 years	12 years

Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Recognized Period

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- Definition

Defined Benefit Plan Corridor Rate

+ References

No definition available.

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- Definition

Defined Benefit Plan Initial Health Care Cost Trend Rate

+ References

No definition available.

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- Details

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- Definition

The interest rate used to adjust for the time value of money.

+ 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 (k)(1)

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

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- Definition

The ultimate trend rate for health care costs.

+ 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 (l)

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

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- Definition

Year the ultimate health care cost trend rate is expected to be reached, in CCYY format.

+ 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 (l)

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

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