Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Plant and Equipment [Line Items]
Plant and equipment at cost	$ 5,305,059	$ 4,931,064
Land and land improvements [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	225,721	209,195
Buildings and improvements [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	581,076	538,712
Plant and equipment, useful life	25 years
Cylinders [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	1,461,600	1,405,857
Plant and equipment, useful life	30 years
Bulk tank stations [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	789,881	720,717
Rental equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	466,833	403,351
Machinery and equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	988,857	948,638
Computers, furniture and fixtures [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	338,316	303,400
Transportation equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	369,034	341,709
Construction in progress [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	$ 83,741	$ 59,485
Minimum [Member] | Bulk tank stations [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	10 years
Minimum [Member] | Rental equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	2 years
Minimum [Member] | Machinery and equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	7 years
Minimum [Member] | Computers, furniture and fixtures [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	3 years
Minimum [Member] | Transportation equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	3 years
Maximum [Member] | Bulk tank stations [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	30 years
Maximum [Member] | Rental equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	10 years
Maximum [Member] | Machinery and equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	10 years
Maximum [Member] | Computers, furniture and fixtures [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	10 years
Maximum [Member] | Transportation equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	15 years
Weighted Average [Member] | Bulk tank stations [Member]
Plant and Equipment [Line Items]
Plant and equipment, useful life	17 years