Loans Receivable and Allowance for Loan Losses (Details 4) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Recorded Investment
Total	$ 11,909,722af_LoansReceivableGrossCarryingAmount	$ 12,386,378af_LoansReceivableGrossCarryingAmount
Residential mortgage loans \| Interest-only loans
Recorded Investment
2015	573,633
2016	415,608
2017	390,439
2018 and thereafter	85,510
Total	$ 1,465,190

Reflects the aggregate gross carrying amount of all categories of loans held in portfolio, prior to deducting deferred income and the allowance for losses on loans.

No definition available.

+ Details

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

- Definition

The aggregate gross carrying amount of interest-only loans held in portfolio, prior to deducting deferred income and the allowance for losses on loans which are scheduled to enter their amortization period within one year from the balance sheet date.

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No definition available.

+ Details

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

- Definition

+ References

No definition available.

+ Details

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

- Definition

+ References

No definition available.

+ Details

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

- Definition

+ References

No definition available.

+ Details

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

- Details

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

- Details

Name:	af_FinancingReceivablesInformationByPortfolioSegmentAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: