Commitments and Contingencies (Sonatide Joint Venture) - Additional Information (Detail) $ in Thousands		3 Months Ended		12 Months Ended
		Jun. 30, 2017 USD ($) Vessel	Jun. 30, 2016 USD ($) Vessel	Mar. 31, 2017 USD ($) Vessel
Commitments and Contingencies Disclosure [Line Items]
Due from affiliate		$ 252,810		$ 262,652
Due to affiliate		121,037		132,857
Commissions payable	[1]	1,867		2,143
Vessel revenues		112,257	$ 162,430
Investments in, at equity, and advances to unconsolidated companies		49,216		45,115
Sonatide joint venture
Commitments and Contingencies Disclosure [Line Items]
Due from affiliate		253,000		263,000
Unpaid vessel revenue		46,000
Due to affiliate		121,000		133,000
Commissions payable		37,500		34,700
Due from affiliate and due to affiliate		$ 21,000
Number of vessels operating | Vessel		7
Number of vessels stacked | Vessel		4
Ownership Interest In Joint Venture		49.00%
Investments in, at equity, and advances to unconsolidated companies		$ 49,000		$ 45,000
Sonatide joint venture | ANGOLA
Commitments and Contingencies Disclosure [Line Items]
Proceeds from related party		15,000
Vessel revenues		$ 27,000	$ 39,000
Percentage of Angolan operation revenue		24.00%	24.00%
Number of vessels operating | Vessel		51	60
Number of vessels stacked | Vessel		22	16
Number of vessels transferred out of Angola | Vessel		1		22
Sonatide joint venture | U.S. dollars initially received by Sonatide on behalf of the company or dollars collected from other customers
Commitments and Contingencies Disclosure [Line Items]
Proceeds from related party		$ 13,000
Sonatide joint venture | Sonatide's converting kwanzas into dollars and subsequent payment to company
Commitments and Contingencies Disclosure [Line Items]
Proceeds from related party		2,000
Sonatide joint venture | Angolan kwanza-denominated
Commitments and Contingencies Disclosure [Line Items]
Bank deposits maintained		$ 84,000

[1] Excludes $37.5 million and $34.7 million of commissions due to Sonatide at June 30, 2017 and March 31, 2017, respectively. These amounts are included in amounts due to affiliate.