Period of time after which participants vest in employer contributions.

No definition available.

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

- Definition

Represents the stated interest rate on loans made to fund the purchase of ESOP shares.

+ References

No definition available.

+ Details

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

- Definition

The outstanding principal balance of the ESOP loan

+ References

No definition available.

+ Details

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

- Definition

Employee Stock Ownership Plan (ESOP), Unallocated Shares Released And Allocated To Participants

+ References

No definition available.

+ Details

Name:	af_EmployeeStockOwnershipPlanESOPUnallocatedSharesReleasedAndAllocatedToParticipants
Namespace Prefix:	af_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum Employer Contribution As A Percent of Employees Compensation

+ References

No definition available.

+ Details

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

- Details

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

- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

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

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

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

- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

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

- Definition

Maximum amount the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

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

- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

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

- Definition

This item represents the amount of cash contributions during the period made by the entity to the Employee Stock Ownership Plan (ESOP).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 40

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929

+ Details

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

- Definition

The amount of plan compensation cost recognized during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 40

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929

+ Details

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

- Definition

The shares or units in an ESOP trust that have been assigned to individual participant accounts based on a known formula. IRS rules require allocations to be nondiscriminatory generally based on compensation, length of service, or a combination of both. For any particular participant such shares or units may be vested, unvested, or partially vested.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 40

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPNumberOfAllocatedShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Details

Name:	us-gaap_DefinedContributionPlanNameAxis=af_IncentiveSavingsPlanAmended2014Scenario1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Benefit Plans (Details 12) (USD $)	0 Months Ended	12 Months Ended			0 Months Ended
Benefit Plans (Details 12) (USD $)	Jan. 01, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 01, 2015
Incentive Savings Plan
Employee maximum contribution of pre-tax base salary, percentage		30.00%
Employee maximum contribution of pre-tax base salary limit		$ 17,500
Maximum percentage of the participating employees' contributions matched by the employer	50.00%
Maximum employer matching contribution as a percentage of participating employees' compensation	6.00%
Maximum Employer Contribution As A Percent of Employees Compensation	3.00%
Matching contributions		2,200,000	2,000,000
Employee vesting in employer contributions after period of time		1 year
Employee Stock Ownership Plan
ESOP loans outstanding principal balance				5,900,000
ESOP loans interest rate (as a percent)			6.00%
Shares allocated to participants			967,013
Shares allocated to participants to date			15,068,562	1,075,354
Cash contribution to participant accounts			155,000	513,000
Compensation expense related to ESOP			$ 11,200,000	$ 10,700,000
Subsequent event
Incentive Savings Plan
Maximum Employer Contribution As A Percent of Employees Compensation					4.50%
Incentive Savings Plan, Amended 2014, Scenario 1 [Member] \| Subsequent event
Incentive Savings Plan
Maximum percentage of the participating employees' contributions matched by the employer					100.00%
Maximum employer matching contribution as a percentage of participating employees' compensation					3.00%
Incentive Savings Plan, Amended 2015, Scenario 2 [Member] \| Subsequent event
Incentive Savings Plan
Maximum percentage of the participating employees' contributions matched by the employer					50.00%
Incentive Savings Plan, Amended 2015, Scenario 2 [Member] \| Minimum \| Subsequent event
Incentive Savings Plan
Maximum employer matching contribution as a percentage of participating employees' compensation					3.00%
Incentive Savings Plan, Amended 2015, Scenario 2 [Member] \| Maximum \| Subsequent event
Incentive Savings Plan
Maximum employer matching contribution as a percentage of participating employees' compensation					6.00%