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Commitments and Contingencies - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended
Jun. 30, 2017
Mar. 31, 2018
Business Acquisition [Line Items]    
Commitments to purchase transportation equipment   $ 217,400,000
WSL    
Business Acquisition [Line Items]    
Initial guaranteed payment $ 0  
Business Combination Consideration Transferred Guaranteed Payment   38,000,000
Former Owner [Member]    
Business Acquisition [Line Items]    
Cash payments   $ 20,000,000
Former Owner [Member] | Minimum    
Business Acquisition [Line Items]    
Business Acquisition Contingent Consideration Discounted Cash Flow Discount Rate   1.00%
Former Owner [Member] | Maximum [Member]    
Business Acquisition [Line Items]    
Business Acquisition Contingent Consideration Discounted Cash Flow Discount Rate   3.00%