Plant and Equipment Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	$ 4,931,064	$ 4,585,933
Land and land improvements [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	209,195	203,362
Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	538,712	511,818
Property, Plant and Equipment, Useful Life	25 years
Cylinders [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	1,405,857	1,360,059
Property, Plant and Equipment, Useful Life	30 years
Bulk tank stations [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	720,717	663,140
Rental equipment [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	403,351	334,844
Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	948,638	897,040
Computers, furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	303,400	277,254
Transportation equipment [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	341,709	312,402
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Plant and equipment at cost	$ 59,485	$ 26,014
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	17 years