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Commitments and Contingencies (Brazilian Customs) - Additional Information (Detail)
pure in Millions, R$ in Millions, $ in Millions
 1 Months Ended 6 Months Ended 9 Months Ended
May 31, 2016
BRL (R$)
Apr. 30, 2011
BRL (R$)
Jun. 30, 2018
USD ($)
Jun. 30, 2018
BRL (R$)
Dec. 31, 2017
USD ($)
Dec. 31, 2017
BRL (R$)
Dec. 31, 2017
BRL (R$)
Commitments and Contingencies Disclosure [Abstract]              
Fines assessed   R$ 33.0 $ 8.5   $ 46.8   R$ 155.0
"Number of Tidewater vessels that the subsidiaries failed to obtain import licenses from | Vessel"   17          
Fines assessed R$ 3.0   0.8   0.9    
Deposit Amount     1.5 R$ 6.0 1.8 R$ 6.0  
Amount of fines contested         9.1 30.0  
Remaining amount of fine resolved in entity favor         $ 36.8 R$ 122.0  
Remaining amount of fines contested     $ 7.7 R$ 30.0