Loans Receivable and Allowance for Loan Losses (Impaired Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
With an allowance recorded:
Related Allowance	$ (12,604)	$ (14,813)
Total impaired loans
Unpaid Principal Balance	262,187	271,192
Recorded Investment	229,459	237,518
Related Allowance	(12,604)	(14,813)
Net Investment	216,855	222,705
Home Equity Lines of Credit \| Home Equity and Other Consumer
With an allowance recorded:
Unpaid Principal Balance	4,796	5,295
Recorded Investment	4,438	4,968
Related Allowance	(370)	(421)
Net Investment	4,068	4,547
Total impaired loans
Related Allowance	(370)	(421)
Mortgage Loans \| Residential \| Full documentation interest-only
With an allowance recorded:
Unpaid Principal Balance	31,384	37,454
Recorded Investment	25,196	30,631
Related Allowance	(3,127)	(4,051)
Net Investment	22,069	26,580
Total impaired loans
Related Allowance	(3,127)	(4,051)
Mortgage Loans \| Residential \| Full documentation amortizing
With an allowance recorded:
Unpaid Principal Balance	82,711	69,242
Recorded Investment	75,484	63,223
Related Allowance	(3,601)	(2,534)
Net Investment	71,883	60,689
Total impaired loans
Related Allowance	(3,601)	(2,534)
Mortgage Loans \| Residential \| Reduced documentation interest-only
With an allowance recorded:
Unpaid Principal Balance	39,060	55,939
Recorded Investment	31,990	46,540
Related Allowance	(2,459)	(4,253)
Net Investment	29,531	42,287
Total impaired loans
Related Allowance	(2,459)	(4,253)
Mortgage Loans \| Residential \| Reduced documentation amortizing
With an allowance recorded:
Unpaid Principal Balance	74,827	57,955
Recorded Investment	66,914	52,520
Related Allowance	(2,879)	(2,310)
Net Investment	64,035	50,210
Total impaired loans
Related Allowance	(2,879)	(2,310)
Mortgage Loans \| Multi-Family
With an allowance recorded:
Unpaid Principal Balance	4,724	8,029
Recorded Investment	4,788	7,950
Related Allowance	(147)	(456)
Net Investment	4,641	7,494
Without an allowance recorded:
Unpaid Principal Balance	9,935	19,523
Recorded Investment	8,712	16,693
Net Investment	8,712	16,693
Total impaired loans
Related Allowance	(147)	(456)
Mortgage Loans \| Commercial Real Estate
With an allowance recorded:
Unpaid Principal Balance	323	6,651
Recorded Investment	344	6,723
Related Allowance	(21)	(788)
Net Investment	323	5,935
Without an allowance recorded:
Unpaid Principal Balance	14,427	11,104
Recorded Investment	11,593	8,270
Net Investment	11,593	8,270
Total impaired loans
Related Allowance	$ (21)	$ (788)

Represents the net amount of investment of impaired financing receivables.

No definition available.

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

- Definition

Represents the net amount of investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

No definition available.

+ Details

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

- Definition

Represents the net amount of investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

No definition available.

+ Details

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

- Definition

Impaired Financing Receivable, Total [Abstract]

+ References

No definition available.

+ Details

Name:	af_ImpairedFinancingReceivableTotalAbstract
Namespace Prefix:	af_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Impaired Financing Receivable, with No Related Allowance [Abstract]

+ References

No definition available.

+ Details

Name:	af_ImpairedFinancingReceivablewithNoRelatedAllowanceAbstract
Namespace Prefix:	af_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Impaired Financing Receivable, with Related Allowance [Abstract]

+ References

No definition available.

+ Details

Name:	af_ImpairedFinancingReceivablewithRelatedAllowanceAbstract
Namespace Prefix:	af_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953550-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRelatedAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=af_ConsumerAndOtherLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_MortgageReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=af_FullDocumentationInterestOnlyLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=af_FullDocumentationAmortizingLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=af_ReducedDocumentationInterestOnlyLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=af_ReducedDocumentationAmortizingLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_MultifamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: