Commitments and Contingencies (Sonatide Joint Venture) - Additional Information (Detail) $ in Thousands		12 Months Ended
		Mar. 31, 2017 USD ($) Vessel	Mar. 31, 2016 USD ($) Vessel	Mar. 31, 2015 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Due from affiliate		$ 262,652	$ 338,595
Due to affiliate		132,857	187,971
Commissions payable	[1]	2,143	7,193
Vessel revenues		$ 583,816	$ 955,400	$ 1,468,358
Number of vessels operating | Vessel		244	253
Investments in, at equity, and advances to unconsolidated companies		$ 45,115	$ 37,502	$ 65,844
Sonatide joint venture
Commitments and Contingencies Disclosure [Line Items]
Due from affiliate		263,000	339,000
Unpaid vessel revenue		56,000
Due to affiliate		133,000	188,000
Commissions payable		34,700	31,600
Due from affiliate and due to affiliate		$ 88,000
Number of vessels operating | Vessel		7
Number of vessels stacked | Vessel		3
Ownership Interest In Joint Venture		49.00%
Investments in, at equity, and advances to unconsolidated companies		$ 45,000	37,000
Sonatide joint venture | ANGOLA
Commitments and Contingencies Disclosure [Line Items]
Proceeds from related party		114,000
Vessel revenues		$ 127,000	$ 213,000
Percentage of Angolan operation revenue		22.00%	22.00%
Number of vessels operating | Vessel		58	65
Number of vessels stacked | Vessel		20	8
Number of vessels transferred out of Angola | Vessel		22	23
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		$ 101,000
Sonatide joint venture | Sonatide's converting kwanzas into dollars and subsequent payment to company
Commitments and Contingencies Disclosure [Line Items]
Proceeds from related party		13,000
Sonatide joint venture | Angolan kwanza-denominated
Commitments and Contingencies Disclosure [Line Items]
Bank deposits maintained		$ 90,000

[1] Excludes $34.7 million and $31.6 million of commissions due to Sonatide at March 31, 2017 and 2016, respectively. These amounts are included in amounts due to affiliates.