DEI Document	6 Months Ended
	Sep. 30, 2014	Nov. 03, 2014
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2014
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2
Trading Symbol	ARG
Entity Registrant Name	AIRGAS INC
Entity Central Index Key	0000804212
Current Fiscal Year End Date	--03-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		74,702,022
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes