Regulatory Matters (Regulatory Capital Requirements) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 risk based capital minimum capital percentage	4.00%
Astoria Financial Corporation
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 leverage		$ 1,471,058
Tier 1 leverage percentage		9.56%
Tier 1 leverage minimum capital requirement		615,813
Tier 1 leverage minimum capital requirement percentage		4.00%
Tier 1 leverage to be well capitalized		769,767
Tier 1 leverage capital to be well capitalized percentage		5.00%
Common equity tier 1		1,347,582
Common equity tier 1 percentage		14.85%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy		408,225
Common equity Tier 1 risk-based capital minimum capital requirement percentage		4.50%
Common equity tier 1 to be well capitalized		589,658
Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets		6.50%
Tier 1 risk based capital		1,471,058
Tier 1 risk based capital percentage		16.22%
Tier 1 risk based capital minimum capital requirement		544,299
Tier 1 risk based capital minimum capital percentage		6.00%
Tier 1 risk based capital to be well capitalized		725,733
Tier 1 risk based capital to be well capitalized percentage		8.00%
Total risk based capital		1,582,466
Total risk based capital percentage		17.44%
Total risk based capital minimum capital requirement		725,733
Total risk based capital minimum capital requirement percentage		8.00%
Total risk based capital to be well capitalized		907,166
Total risk based capital to be well capitalized percentage		10.00%
Astoria Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 leverage		1,629,273
Tier 1 leverage percentage		10.63%
Tier 1 leverage minimum capital requirement		613,074
Tier 1 leverage minimum capital requirement percentage		4.00%
Tier 1 leverage to be well capitalized		766,343
Tier 1 leverage capital to be well capitalized percentage		5.00%
Common equity tier 1		1,629,273
Common equity tier 1 percentage		18.00%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy		407,380
Common equity Tier 1 risk-based capital minimum capital requirement percentage		4.50%
Common equity tier 1 to be well capitalized		588,438
Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets		6.50%
Tier 1 risk based capital		1,629,273
Tier 1 risk based capital percentage		18.00%
Tier 1 risk based capital minimum capital requirement		543,173
Tier 1 risk based capital minimum capital percentage		6.00%
Tier 1 risk based capital to be well capitalized		724,231
Tier 1 risk based capital to be well capitalized percentage		8.00%
Total risk based capital		1,740,681
Total risk based capital percentage		19.23%
Total risk based capital minimum capital requirement		724,231
Total risk based capital minimum capital requirement percentage		8.00%
Total risk based capital to be well capitalized		$ 905,289
Total risk based capital to be well capitalized percentage		10.00%

Common Equity Tier 1 Risk Based Capital Required to be Well Capitalized

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Common Equity Tier 1 capital divided by risk weighted assets as defined by regulations.

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Common Equity Tier One Risk Based Capital

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Common Equity Tier One Risk Based Capital Required for Capital Adequacy

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The minimum common equity Tier 1 Risk Based Capital ratio (common equity tier 1 capital divided by risk weighted assets) required for capital adequacy purposes in the regulatory framework for prompt corrective action.

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The common equity Tier 1 capital ratio (common equity tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" in the regulatory framework for prompt corrective action.

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The amount of total capital as defined in the regulations.

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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