Deferred Costs - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2015	Feb. 28, 2014
Deferred Costs [Abstract]
Allowance for deferred costs related to supply agreements	$ 2,300am_AllowanceForDeferredCosts	$ 4,100am_AllowanceForDeferredCosts

Allowance included in other assets for deferred costs related to retail supply agreements.

No definition available.

Name:	am_AllowanceForDeferredCosts
Namespace Prefix:	am_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant