Plant and Equipment Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	$ 4,585,933	$ 4,306,420
Land and land improvements [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	203,362	184,522
Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	511,818	470,561
Property, Plant and Equipment, Useful Life	25 years
Cylinders [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	1,360,059	1,335,113
Property, Plant and Equipment, Useful Life	30 years
Bulk tank stations [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	663,140	613,011
Rental equipment [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	334,844	275,285
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	897,040	826,949
Computers, furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	277,254	254,178
Transportation equipment [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	312,402	288,678
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	$ 26,014	$ 58,123
Minimum [Member] | Bulk tank stations [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Minimum [Member] | Rental equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Minimum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Minimum [Member] | Computers, furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Minimum [Member] | Transportation equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Maximum [Member] | Bulk tank stations [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	30 years
Maximum [Member] | Rental equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Maximum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Maximum [Member] | Computers, furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Maximum [Member] | Transportation equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	15 years
Weighted Average [Member] | Bulk tank stations [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	16 years