Merger - Additional Information (Detail) (USD $)	12 Months Ended
Feb. 28, 2015
Business Combinations [Abstract]
Offer price to convert common shares held by the shareholders (except family shareholders) of the Corporation	$ 19.00us-gaap_SharePrice
Consideration received by family shareholders	$ 0

Common shares held by the Family Shareholders reacquired for no consideration pursuant to the Merger Agreement.

No definition available.

Name:	am_BusinessCombinationConsiderationReceivedByFamilyShareholders
Namespace Prefix:	am_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration