v3.8.0.1

Commitments and Contingencies - Surety Bonds (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Surety Bonds |  |
Commitments and Contingencies |  |
Loss contingency on certain claims | $ 36.1 | $ 30.6

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- Definition 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. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Definition Reflects the estimated amount of loss from the specified contingency as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |