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Financial Statement Details - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]    
Vehicles and equipment under capital leases, net $ 1.9 $ 1.6
Vehicles and equipment under capital leases, accumulated depreciation (2.0) (1.5)
Depreciation and amortization expense $ 7.0 $ 8.0