Commitments and Contingencies (Details) $ in Millions	Jun. 30, 2018 USD ($)
Commitments and Contingencies
Purchase orders outstanding for equipment, parts and supplies	$ 97.5
Contingencies
Gain contingencies recognized in consolidated financial statements	$ 0.0

Amount of gain recognized in the period that had been disclosed in prior periods as a contingent gain.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6397426&loc=d3e17499-108355

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant