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Commitments and Contingencies - Additional Information (Detail)
$ in Thousands
 6 Months Ended 12 Months Ended
Sep. 30, 2017
USD ($)
Vessel
T
Mar. 31, 2016
USD ($)
Jul. 31, 2017
USD ($)
Significant Purchase and Supply Commitment [Line Items]      
Accumulated costs of rejected vessel [1] $ 7,007    
Fast, Crew/Supply Boat      
Significant Purchase and Supply Commitment [Line Items]      
Number of vessels under construction | Vessel 1    
Remaining accumulated cost reclassified from construction in progress to other assets as insurance receivable   $ 5,600  
Remaining insurance receivable $ 1,800   $ 1,800
Vessel Commitments      
Significant Purchase and Supply Commitment [Line Items]      
Remaining Balance, commitments $ 5,500    
Number of Vessels, commitments | Vessel 1    
Significant commitment, new construction deadweight tons capacity | T 5,400    
Refund amount demanded to shipyard $ 43,000    
Accumulated costs of rejected vessel 48,700    
Value of each vessels $ 7,000    
[1] Refer to Note (10) of Notes to Condensed Consolidated Financial Statements for additional information regarding the vessel rejected at the time of delivery.