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	3 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Mar. 31, 2014
Consideration [Abstract]
Cash	$ 23,463		$ 5,143
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Goodwill	1,304,587			1,289,896
Distribution Business Segment [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Goodwill	1,107,377			1,092,728
FY15 Acquisitions [Member] | Distribution Business Segment [Member]
Consideration [Abstract]
Cash	23,463	[1]
Airgas, Inc. common stock	4,458	[2]
Fair value of total consideration transferred	27,921
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Current assets, net	6,697
Plant and equipment	7,238
Other intangible assets	7,668
Current liabilities	(5,582)
Non-current liabilities	(2,258)
Total identifiable net assets	13,763
Goodwill	14,158
Business combination, recognized identifiable assets acquired, goodwill, and liabilities assumed, net	$ 27,921
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 market price of Airgas, Inc. common stock on the acquisition date.