Deferred Costs - Additional Information (Detail) - USD ($) $ in Millions	Aug. 26, 2016	Feb. 29, 2016	Aug. 28, 2015
Deferred Costs [Abstract]
Allowance for deferred costs related to supply agreements	$ 3.2	$ 3.6	$ 3.5

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