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Commitments and Contingencies (Brazilian Customs) - Additional Information (Detail)
BRL in Millions, $ in Millions
 1 Months Ended 6 Months Ended
May 31, 2016
BRL
Apr. 30, 2011
BRL
Vessel
Sep. 30, 2017
USD ($)
Sep. 30, 2017
BRL
Commitments And Contingencies Disclosure [Abstract]        
Fines assessed   BRL 155 $ 49.0  
Number of Tidewater vessels that the subsidiaries failed to obtain import licenses from | Vessel   17    
Fines assessed BRL 3   0.9  
Deposit Amount     1.9 BRL 6
Amount of fines contested     9.5 30
Remaining amount of fine resolved in entity favor     $ 38.6 122
Original fine amount | BRL       BRL 155