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Rego Park II Apartment Tower (Details) (Rego Park 2 Property [Member], USD $) | Sep. 30, 2013 sqft property
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Rego Park 2 Property [Member] |
Real Estate Properties [Line Items] |
Approximate Number Of Apartment Units | 300
Area Of Real Estate Property (square feet) | 250,000
Estimated future funding | $ 125,000,000

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- Definition Estimated future funding for proposed development. + References No definition available. + Details
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Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Area of a real estate property. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | instant

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- Definition The number of units in a real estate property owned as of the balance sheet date. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: | us-gaap_
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Period Type: | duration