Benefit Plans (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Benefit Plans
Increase in funded status	$ 40.6
Decrease in the projected benefit obligation	20.4
Increase in the fair value of plan assets	$ 20.2

The change in the projected benefit plan obligation from the prior year end.

No definition available.

Name:	af_DefinedBenefitPlanChangeInProjectedBenefitObligation
Namespace Prefix:	af_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant