Details of Number of Vessels, Total Proceeds, Carrying Values at the Time of Sale, Deferred Gains Recognized, Lease Expirations, and Contractual Purchase Option (Detail) (USD $)
In Thousands, unless otherwise specified

Details of Number of Vessels, Total Proceeds, Carrying Values at the Time of Sale, Deferred Gains Recognized, Lease Expirations, and Contractual Purchase Option (Detail) (USD $) In Thousands, unless otherwise specified	1 Months Ended					3 Months Ended							12 Months Ended
	Mar. 31, 2015 Vessel	Mar. 31, 2014 Vessel	Jul. 31, 2009 Vessel	Jun. 30, 2009 Vessel	Mar. 31, 2006	Mar. 31, 2015 Vessel	Dec. 31, 2014 Vessel	Sep. 30, 2014 Vessel	Jun. 30, 2014 Vessel	Mar. 31, 2014 Vessel	Dec. 31, 2013 Vessel	Sep. 30, 2013 Vessel	Mar. 31, 2015 Vessel	Mar. 31, 2014 Vessel	Mar. 31, 2010
Sale Leaseback Transaction [Line Items]
Number of Vessels	2	3	6	6		1	3	1	1	4	4	2	6	10
Total Proceeds					$ 76,500	$ 13,000	$ 78,200	$ 19,350	$ 13,400	$ 63,305	$ 141,900	$ 65,550	$ 123,950	$ 270,755	$ 101,800
Carrying Value at time of Sale						5,115	33,233	8,214	4,002	32,845	105,649	34,325	50,564	172,819
Deferred Gain at time of Sale						$ 7,885	$ 44,967	$ 11,136	$ 9,398	$ 30,460	$ 36,251	$ 31,225	$ 73,386	$ 97,936
Lease Term in Years						7 years		8 years 6 months	7 years			7 years
Purchase Option Percentage						50.00%	60.00%	47.00%	61.00%			55.00%
Purchase Option at end of:						6thYear	7th or 8th Year	8thYear	6th Year	6th or 9th Year	6th or 8th Year	6th Year
Minimum
Sale Leaseback Transaction [Line Items]
Lease Term in Years							8 years			7 years	7 years
Purchase Option Percentage										53.00%	54.00%
Maximum
Sale Leaseback Transaction [Line Items]
Lease Term in Years							9 years			10 years	9 years
Purchase Option Percentage										59.00%	68.00%