PROPERTY AND EQUIPMENT (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012
Property, Plant and Equipment [Line Items]
Cost	$ 252,292	$ 245,911
Accumulated depreciation	48,021	45,049
Property and equipment, net	204,271	200,862
Acquired vessel included in property and equipment not yet in use	27	21,927
Vessels [Member]
Property, Plant and Equipment [Line Items]
Cost	245,328	238,830
Accumulated depreciation	45,279	42,426
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	3,779	3,847
Accumulated depreciation	1,087	1,034
Furniture and equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	329	335
Accumulated depreciation	168	162
Vehicles [Member]
Property, Plant and Equipment [Line Items]
Cost	22	21
Accumulated depreciation	12	12
Computer, communication equipment and purchased software [Member]
Property, Plant and Equipment [Line Items]
Cost	2,834	2,878
Accumulated depreciation	$ 1,475	$ 1,415