Schedule of Target Assets Allocation (Detail)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	100.00%
Total	100.00%	100.00%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	54.00%
Total	57.00%	57.00%
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	30.00%
Total	29.00%	28.00%
Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	8.00%
Total	7.00%	7.00%
Real Estate
Defined Benefit Plan Disclosure [Line Items]
Other securities, Target Allocation	8.00%
Total	7.00%	8.00%

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one 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 (d)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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