Commitments and Contingencies (Collective Bargaining Agreements and Multiemployer Plans) (Narrative) (Details) - Central States [Member] - Multiemployer Plans, Pension [Member] - USD ($) $ in Millions	12 Months Ended	72 Months Ended
Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2011
Loss Contingencies [Line Items]
Multiemployer plan, withdrawal liability, amount			$ 6.4
Multiemployer plan, withdrawal liability, payments		$ 6.4
Multiemployer plan, withdrawal liability, expense	$ 0.7

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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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 charged against operating income increasing loss contingency liability, after adjustments to reduce previously estimated charges.

+ References

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- Definition

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.

+ References

No definition available.

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