Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Revenue, PPE, Insurance and Other (Details)

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Summary of Significant Accounting Policies - Revenue, PPE, Insurance and Other (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Insurance receivables      
Insurance receivables $ 2.0 $ 3.2  
Insurance Liabilities      
Insurance liability 2.0 3.2  
Advertising      
Advertising expense $ 1.1 1.1 $ 1.5
Buildings and land improvements | Minimum      
Property and Equipment      
Estimated Useful Life (in years) 20 years    
Buildings and land improvements | Maximum      
Property and Equipment      
Estimated Useful Life (in years) 40 years    
Software | Minimum      
Property and Equipment      
Estimated Useful Life (in years) 3 years    
Software | Maximum      
Property and Equipment      
Estimated Useful Life (in years) 6 years    
Company vehicles | Minimum      
Property and Equipment      
Estimated Useful Life (in years) 3 years    
Company vehicles | Maximum      
Property and Equipment      
Estimated Useful Life (in years) 8 years    
Equipment | Minimum      
Property and Equipment      
Estimated Useful Life (in years) 6 years    
Equipment | Maximum      
Property and Equipment      
Estimated Useful Life (in years) 10 years    
Installation | Unbilled Revenues      
Revenue Recognition      
Revenues $ 37.1 $ 28.9