Inventories, Net (Details) (USD $)	Dec. 31, 2011	Mar. 31, 2011
Inventories [Line Items]
Inventories, net	$ 393,363,000	$ 362,502,000
Hardgoods [Member]
Inventories [Line Items]
Inventories, net	292,644,000	246,607,000
LIFO inventory amount	36,000,000	32,000,000
Excess carrying value of inventories when valued under FIFO	12,000,000	11,100,000
Gases [Member]
Inventories [Line Items]
Inventories, net	$ 100,719,000	$ 115,895,000