Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Plant and Equipment [Line Items]
Plant and equipment at cost	$ 5,559,041	$ 5,305,059
Land and land improvements [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	246,820	225,721
Buildings and improvements [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	$ 634,816	581,076
Plant and equipment, useful life	25 years
Cylinders [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	$ 1,504,566	1,461,600
Plant and equipment, useful life	30 years
Bulk tank stations [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	$ 846,344	789,881
Rental equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	496,383	466,833
Machinery and equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	1,057,142	988,857
Computers, furniture and fixtures [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	296,408	338,316
Transportation equipment [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	366,221	369,034
Construction in progress [Member]
Plant and Equipment [Line Items]
Plant and equipment at cost	$ 110,341	$ 83,741
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