Schedule of Vessel Commitments (Detail) $ in Thousands		1 Months Ended		12 Months Ended
		Sep. 30, 2015 Vessel	Apr. 30, 2015 Vessel	Mar. 31, 2016 USD ($) Vessel		May. 31, 2015 USD ($)
Significant Purchase and Supply Commitment [Line Items]
Number of Vessels, commitments | Vessel				6
Number of vessels under construction | Vessel		9
Vessel Commitments
Significant Purchase and Supply Commitment [Line Items]
Number of Vessels, commitments | Vessel	[1]			6
Total cost, commitments	[1]			$ 251,420
Invested, commitments	[1]			183,904
Remaining Balance, commitments	[1]			$ 67,516
Deepwater PSVs
Significant Purchase and Supply Commitment [Line Items]
Number of vessels under construction | Vessel		6	2	6	[1]
Total cost, under construction	[1]			$ 251,420
Invested, under construction				183,904	[1]	$ 5,400
Remaining Balance, under construction	[1]			$ 67,516

[1] (A) Six additional option vessels and a fast supply boat are not included in the table above.