Indebtedness (Senior Credit Facility Narrative) (Details) In Millions, unless otherwise specified	3 Months Ended
Jun. 30, 2014 Revolving credit facility [Member] USD ($)	Jun. 30, 2014 Revolving credit borrowings - US [Member] USD ($)	Jun. 30, 2014 Revolving credit borrowings - multi-currency [Member] USD ($)	Jun. 30, 2014 Revolving credit borrowings - France [Member] USD ($)	Jun. 30, 2014 Revolving credit borrowings - France [Member] EUR (€)	Jun. 30, 2014 Maximum [Member] Revolving credit facility [Member] USD ($)
Debt Instrument [Line Items]
Revolving line of credit, maximum borrowing capacity	$ 750.0	$ 650.0	$ 100.0	$ 11.0	€ 8.0
Letters of credit sublimit						65
Debt swingline sublimit						50
Credit facility, expiration date	Jul. 19, 2016	Jul. 19, 2016	Jul. 19, 2016	Jul. 19, 2016	Jul. 19, 2016
Revolving credit facility, maximum increase	325		50
Revolver, outstanding borrowings	57.0	0	57.0	8.0	5.8
Letters of credit outstanding		51
Basis spread on variable rate		1.25%	1.25%	1.25%	1.25%
Revolving credit facility, interest rate at period end			1.76%	1.48%	1.48%
Revolving credit facility, unused capacity, commitment fee percentage		0.20%	0.20%
Remaining availability under revolving credit facility	$ 590

Debt Swingline, Sublimit, maximum amount of funds the Company can borrow to repay other outstanding debt

No definition available.

Name:	arg_DebtSwinglineSublimit
Namespace Prefix:	arg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Letters of Credit, Sublimit, maximum amount of debt allowed under LOCs

+ References

No definition available.

+ Details

Name:	arg_LettersofCreditSublimit
Namespace Prefix:	arg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line Of Credit Facility, Increase, Additional Borrowings, Maximum

+ References

No definition available.

+ Details

Name:	arg_LineOfCreditFacilityIncreaseAdditionalBorrowingsMaximum
Namespace Prefix:	arg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount borrowed under the credit facility as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective interest rate at the end of the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration