Acquisitions (Summary of the Consideration Transferred and the Fair Values of the Assets Acquired and Liabilities Assumed) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
	Sep. 30, 2014		Sep. 30, 2013	Mar. 31, 2014
Consideration
Cash	$ 29,834		$ 15,745
Recognized amounts of identifiable assets acquired and liabilities assumed
Goodwill	1,309,247			1,289,896
FY15 Acquisitions [Member]
Consideration
Cash	29,834	[1]
Airgas, Inc. common stock	4,458	[2]
Fair value of total consideration transferred	34,292
Recognized amounts of identifiable assets acquired and liabilities assumed
Current assets, net	7,751
Plant and equipment	8,943
Other intangible assets	9,411
Current liabilities	(7,333)
Non-current liabilities	(4,423)
Total identifiable net assets	14,349
Goodwill	19,943
Recognized amounts of identifiable assets acquired, goodwill, and liabilities assumed, net	$ 34,292
Number of shares of Airgas, Inc. common stock issued in connection with an acquisition	41,060

[1] Includes cash paid, net of cash acquired, for current year acquisitions as well as payments for the settlement of holdback liabilities and contingent consideration arrangements associated with prior year acquisitions.

[2] Represents 41,060 shares of Airgas, Inc. common stock issued in connection with a single acquisition. The fair value of the shares issued as part of the consideration for the acquisition was determined based on the closing sales price of Airgas, Inc. common stock on the acquisition date.