Represents the fixed rate period for amortizing hybrid adjustable rate mortgages.

No definition available.

Name:	af_AmortizingHybridAdjustableRateMortgageFixedRatePeriod
Namespace Prefix:	af_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the chapter 7 bankruptcy loans classified as troubled debt restructurings to comply with regulatory guidance issued in 2012 and are included in non-accrual loans.

+ References

No definition available.

+ Details

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

- Definition

Represents loans modified in troubled debt restructurings less than 90 days past due included in non-accrual loans.

+ References

No definition available.

+ Details

Name:	af_FinancingReceivableModificationsPostModificationRecordedInvestmentLessThan90DaysPastDue
Namespace Prefix:	af_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the value of accruing loans.

+ References

No definition available.

+ Details

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

- Definition

Amount of interest income that would have been recorded if nonperforming loans were instead current and in compliance with their original terms

+ References

No definition available.

+ Details

Name:	af_LoansAndLeasesReceivableNonPerformingLoansInterestThatWouldHaveBeenRecognized
Namespace Prefix:	af_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of total loans.

+ References

No definition available.

+ Details

Name:	af_PercentageOfTotal
Namespace Prefix:	af_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13537-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5111-111524

+ Details

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

- Definition

Average 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 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.8)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 8

-Article 5

+ Details

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

- Definition

Interest received on loans and other debt instruments during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 27

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3536-108585

+ Details

Name:	us-gaap_ProceedsFromInterestReceived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Loans Receivable and Allowance for Loan Losses (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Loans receivable and allowance for loan losses
Accrued interest receivable	$ 41,688,000	$ 46,528,000
Loans (gross) amount	13,155,914,000	13,197,560,000
Average recorded investment in impaired loans	342,760,000	309,898,000	270,600,000
Interest income recognized on impaired loans	9,781,000	8,910,000	8,600,000
Impaired loans, cash basis interest income	10,212,000	9,257,000	9,400,000
Loans in non-accrual status	314,758,000	332,695,000
Modified in troubled debt restructuring
Loans receivable and allowance for loan losses
Loans less than 90 days past due included in non-accrual loans	13,700,000	10,900,000
Loans in non-accrual status	32,800,000	18,800,000
Chapter 7 bankruptcy loans classified as troubled debt restructurings	12,500,000
Accruing loans	98,700,000	73,700,000
Residential \| Geographic Concentration Risk \| Minimum
Loans receivable and allowance for loan losses
Percentage threshold for reporting concentrations	5.00%
Residential \| Geographic Concentration Risk \| Florida
Loans receivable and allowance for loan losses
Percentage threshold for reporting concentrations	1.80%
Residential \| Period 1
Loans receivable and allowance for loan losses
Amortizing hybrid ARM fixed rate period	3 years
Residential \| Period 2
Loans receivable and allowance for loan losses
Amortizing hybrid ARM fixed rate period	5 years
Residential \| Period 3
Loans receivable and allowance for loan losses
Amortizing hybrid ARM fixed rate period	7 years
Residential \| Period 4
Loans receivable and allowance for loan losses
Amortizing hybrid ARM fixed rate period	10 years
Multi Family and Commercial Real Estate Mortgage Loan \| New York Metropolitan Area
Loans receivable and allowance for loan losses
Percentage of Total	97.00%
Multi Family and Commercial Real Estate Mortgage Loan \| Other State
Loans receivable and allowance for loan losses
Percentage of Total	3.00%
Non-performing
Loans receivable and allowance for loan losses
Non-accrual loans, interest that would have been recognized	16,800,000	19,300,000	24,000,000
Actual payment recorded as interest income	4,300,000	5,200,000	8,800,000
Non-performing \| Residential \| Geographic Concentration Risk \| Florida
Loans receivable and allowance for loan losses
Percentage threshold for reporting concentrations	6.20%
Non-performing \| Multi Family and Commercial Real Estate Mortgage Loan \| New York Metropolitan Area
Loans receivable and allowance for loan losses
Percentage of Total	97.00%
Non-performing \| Multi Family and Commercial Real Estate Mortgage Loan \| Florida
Loans receivable and allowance for loan losses
Percentage of Total	3.00%
Fiscal Year Pre 4Q 2010 \| Residential \| Period 1
Loans receivable and allowance for loan losses
Amortizing hybrid ARM fixed rate period	3 years
Fiscal Year Pre 4Q 2010 \| Residential \| Period 2
Loans receivable and allowance for loan losses
Amortizing hybrid ARM fixed rate period	5 years
Fiscal Year Pre 4Q 2010 \| Residential \| Period 3
Loans receivable and allowance for loan losses
Amortizing hybrid ARM fixed rate period	7 years
Total loans
Loans receivable and allowance for loan losses
Accrued interest receivable	36,000,000	39,000,000
Mortgage Loans (Gross)
Loans receivable and allowance for loan losses
Loans (gross) amount	12,891,820,000	12,915,116,000
Loans in non-accrual status	308,250,000	326,627,000
Mortgage Loans (Gross) \| Residential
Loans receivable and allowance for loan losses
Loans (gross) amount	9,711,226,000	10,561,539,000
Loans in non-accrual status	291,051,000	317,853,000
Mortgage Loans (Gross) \| Residential \| Pre 2007 Interest Only Loans
Loans receivable and allowance for loan losses
Loans (gross) amount	2,180,000,000	2,500,000,000
Mortgage Loans (Gross) \| Residential \| Reduced Documentation Loans
Loans receivable and allowance for loan losses
Loans (gross) amount	1,400,000,000	1,560,000,000
Mortgage Loans (Gross) \| Residential \| Reduced Documentation Loans \| SISA (stated income, stated asset) loans
Loans receivable and allowance for loan losses
Loans (gross) amount	222,700,000	240,700,000
Mortgage Loans (Gross) \| Multi-Family
Loans receivable and allowance for loan losses
Loans (gross) amount	2,406,678,000	1,693,871,000
Loans in non-accrual status	10,658,000	7,874,000
Mortgage Loans (Gross) \| Commercial Real Estate
Loans receivable and allowance for loan losses
Loans (gross) amount	773,916,000	659,706,000
Loans in non-accrual status	$ 6,541,000	$ 900,000