Commitments and Contingencies - Additional Information (Detail) $ in Thousands			1 Months Ended			3 Months Ended	6 Months Ended			12 Months Ended
		Mar. 31, 2016 USD ($)	Oct. 31, 2016 USD ($)	Jun. 30, 2015 Vessel T hp	May 31, 2015 USD ($) Vessel T	Jun. 30, 2016 USD ($)	Sep. 30, 2016 USD ($) Vessel T hp		Sep. 30, 2015 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)
Significant Purchase and Supply Commitment [Line Items]
Refunds from cancelled vessel construction contracts							$ 11,515		$ 36,190
Fast, Crew/Supply Boat
Significant Purchase and Supply Commitment [Line Items]
Number of vessels under construction | Vessel							1
Impairment charge on amounts not recoverable							$ 2,400
Insurance coverage for the progress payments made on the vessel by the third party credit support							90.00%
Insurance coverage by the third party credit support for the carrying value of the accumulated costs							$ 2,400
Fast, Crew/Supply Boat | Reclassification of Construction in Progress to Other Non-Current Assets
Significant Purchase and Supply Commitment [Line Items]
Committed and invested amount, remaining							5,600
Vessel Commitments
Significant Purchase and Supply Commitment [Line Items]
Remaining Balance, commitments	[1]						$ 47,974
Number of Vessels, commitments | Vessel	[1]						3
Unfunded capital commitment, net of expected refunds							$ 33,700
Expected refunds from shipyards							$ 14,300
Deepwater PSVs
Significant Purchase and Supply Commitment [Line Items]
Significant commitment, new construction deadweight tons capacity range, low | T							4,700
Significant commitment, new construction deadweight tons capacity range, high | T							5,400
Number of vessels under construction | Vessel					2		3	[2]
Significant commitment, new construction deadweight tons capacity | T					3,800
Refunds from cancelled vessel construction contracts							$ 19,100
Impairment charge on amounts not recoverable						$ 1,900
Aggregate installment payment					$ 5,400		$ 115,683	[2]
Obligation to be relieved					21,700
Aggregate installment payment payment with interest					$ 11,900
Shipyard returned to the company						11,500
Shipyard owed amount						11,700
Foreign taxes on interest						200
Remaining installment obligation held						$ 250
Extended option period for vessels							Dec. 31, 2016
Deepwater PSVs | Subsequent Event
Significant Purchase and Supply Commitment [Line Items]
Net payment to company on vessel construction			$ 14,000
Vessels Under Construction
Significant Purchase and Supply Commitment [Line Items]
Number of vessels under construction | Vessel				6			6
Significant commitment, new construction brake horsepower | hp				7,145			7,145
Significant commitment, new construction deadweight tons capacity | T				4,700			4,700
Deferred final installment of vessel construction contracts		$ 5,100
Refunds from cancelled vessel construction contracts											$ 36,000
Obligation to pay additional amount due to termination											50,000
Accrued interest owing on the returned installments		$ 3,500									3,500
Impairment charge on amounts not recoverable											$ 800
Vessels Under Construction | Scenario Forecast
Significant Purchase and Supply Commitment [Line Items]
Refunds from cancelled vessel construction contracts										$ 26,000
Obligation to pay additional amount due to termination										35,000
Accrued interest owing on the returned installments										$ 3,800
Minimum | Deepwater PSVs
Significant Purchase and Supply Commitment [Line Items]
Significant commitment, new construction final delivery date							2017-02
Maximum | Deepwater PSVs
Significant Purchase and Supply Commitment [Line Items]
Significant commitment, new construction final delivery date							2017-06

[1] The company is entitled to receive a refund of prior shipyard payments totaling $14.3 million which would reduce the remaining balance of vessel commitments. See further discussion below.

[2] Six additional option vessels and a fast supply boat are not included in the table above.