Schedule of Aggregate Amount of Senior Unsecured Notes Outstanding (Detail) - USD ($) $ in Thousands		12 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Debt [Line Items]
Debt instrument outstanding amount		$ 2,052,270	$ 1,534,476
Notes Due April 2027 | Troms Offshore Supply AS
Debt [Line Items]
Fair value of debt outstanding	[1]	30,062
Debt instrument outstanding amount	[1]	30,033
Notes Due January 2027 | Troms Offshore Supply AS
Debt [Line Items]
Fair value of debt outstanding	[1]	27,027	29,501
Debt instrument outstanding amount	[1]	27,030	29,488
September 2013 Senior Unsecured Notes
Debt [Line Items]
Aggregate debt outstanding		$ 500,000	$ 500,000
Weighted average remaining life in years		7 years 4 months 24 days	8 years 4 months 24 days
Weighted average coupon rate on notes outstanding		4.86%	4.86%
Fair value of debt outstanding		$ 342,746	$ 516,879
August 2011 Senior Unsecured Notes
Debt [Line Items]
Aggregate debt outstanding		$ 165,000	$ 165,000
Weighted average remaining life in years		4 years 7 months 6 days	5 years 7 months 6 days
Weighted average coupon rate on notes outstanding		4.42%	4.42%
Fair value of debt outstanding		$ 127,148	$ 167,910
September 2010 Senior Unsecured Notes
Debt [Line Items]
Aggregate debt outstanding		$ 382,500	$ 425,000
Weighted average remaining life in years		4 years 1 month 6 days	4 years 7 months 6 days
Weighted average coupon rate on notes outstanding		4.35%	4.25%
Fair value of debt outstanding		$ 302,832	$ 431,296
July 2003 Senior Unsecured Notes
Debt [Line Items]
Aggregate debt outstanding			$ 35,000
Weighted average remaining life in years		0 years	3 months 18 days
Weighted average coupon rate on notes outstanding			4.61%
Fair value of debt outstanding			$ 35,197

[1] Note requires semi-annual principal payments.