Annual report pursuant to Section 13 and 15(d)

Property and Equipment, net - Additional Information (Details)

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Property and Equipment, net - Additional Information (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Capital Leased Assets [Line Items]      
Depreciation and amortization expense $ 19.5 $ 18.8 $ 11.2
Vehicles      
Capital Leased Assets [Line Items]      
Gross amount of assets under capital leases 44.8 46.2  
Accumulated depreciation for assets under capital leases 26.1 16.3  
Depreciation of capital leased asset $ 10.9 $ 10.8 $ 4.9