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Commitments and Contingencies (Brazilian Customs) - Additional Information (Detail) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended
	Apr. 30, 2011 BRL Vessel	Sep. 30, 2014 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2014 BRL	Sep. 30, 2014 Revised USD ($)	Sep. 30, 2014 Revised BRL
Commitments and Contingencies Disclosure [Line Items]
Fines assessed	155.0		$ 63.6		$ 52.1	127.0
Number of Tidewater vessels that the subsidiaries failed to obtain import licenses from	17
Disallowed amount of total fines by the administrative appeals board		61.1		149.0
Remaining amount of fines contested		11.5		28.0
Decision disallowing the fines totaling				127.0