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Legal Matters - Additional Information (Detail) - Robles Lawsuits [Member]
12 Months Ended
Aug. 05, 2015
Plaintiff
Employee
May 15, 2015
Plaintiff
Dec. 31, 2017
Loss Contingencies [Line Items]      
Percentage of California drivers who accepted settlement offers     96.00%
Number of plaintiffs   2  
Number of plaintiffs against HGT 63    
Number of claims signed settlement agreements 58    
Hub And HGT [Member]      
Loss Contingencies [Line Items]      
Number of employees filed lawsuit | Employee 5