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Commitments and Contingencies - Collective Bargaining Agreements (Detail) - Withdrawal from Multiemployer Defined Benefit Plan - Central States Plan - USD ($) $ in Millions	36 Months Ended	52 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Jan. 31, 2016	Jul. 31, 2014	Oct. 09, 2013	Dec. 31, 2011
Loss Contingencies [Line Items]
Amount of withdrawal liability			$ 32.9	$ 39.6		$ 32.6
Payment of withdrawal liability assessment amount	$ 22.3
Acquired Company
Loss Contingencies [Line Items]
Amount of withdrawal liability			$ 4.8		$ 4.8
Payment of withdrawal liability assessment amount		$ 4.0
Amount of withdrawal liability, amount suggested by Plan which is different than amount recorded by company					$ 6.9
Minimum
Loss Contingencies [Line Items]
Amount of withdrawal liability	42.2	42.2
Maximum
Loss Contingencies [Line Items]
Amount of withdrawal liability	$ 48.2	$ 48.2

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Multiemployer Plan Withdrawal Obligation Amount Suggested By Plan Different Than Amount Recorded By Company

+ References

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- Definition

Amount of cash outflow reducing loss contingency liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

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Amount of the obligation recognized by withdrawing from a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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