XML 77 R42.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Rego Park II Apartment Tower (Details) (Rego Park 2 Property [Member], USD $) | Jun. 30, 2013 sqft property
--- | ---
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

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

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

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

X
- Details
Name: | us-gaap_RealEstatePropertiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration