Schedule of Asset Allocation Policy and Ranges for Overall Risk and Return Objectives of Portfolio (Detail)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Assets allocation	100.00%	100.00%
Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Assets allocation	23.00%
Permitted Range, minimum	10.00%
Permitted Range, maximum	30.00%
Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Assets allocation	75.00%
Permitted Range, minimum	70.00%
Permitted Range, maximum	90.00%
Other
Defined Benefit Plan Disclosure [Line Items]
Assets allocation	2.00%	2.00%
Permitted Range, minimum	0.00%
Permitted Range, maximum	10.00%

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Target allocation of investments of this type to total plan assets presented on a weighted average basis.

+ 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)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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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)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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-Name Accounting Standards Codification
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