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Schedule III: Real estate and Accumulated depreciation (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | $ 1,032,780 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances |  |  |
Initial cost of Land | 21,593 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand |  |  |
Initial cost of Building, Leaseholds and Leasehold improvements | 26,239 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements |  |  |
Costs capitalized subsequent to acquisition | 946,095 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements |  |  |
Carrying amount of Land | 44,971 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand |  |  |
Carring amount of Building, Leaseholds and Leasehold improvements | 873,667 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements |  |  |
Construction in progress | 75,289 alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress |  |  |
Total | 993,927 us-gaap_RealEstateGrossAtCarryingValue | 919,576 us-gaap_RealEstateGrossAtCarryingValue | 911,792 us-gaap_RealEstateGrossAtCarryingValue | 906,907 us-gaap_RealEstateGrossAtCarryingValue
Accumulated depreciation and amortization | 210,025 us-gaap_RealEstateAccumulatedDepreciation | 185,375 us-gaap_RealEstateAccumulatedDepreciation | 160,826 us-gaap_RealEstateAccumulatedDepreciation | 136,460 us-gaap_RealEstateAccumulatedDepreciation
Differences Between Book and Tax Basis | 204,815 alx_CumulativeAmountOfTemporaryDifferenceBetweenBookValueAndTaxBasis |  |  |
Lexington Avenue Property [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 620,000 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_LexingtonAvenuePropertyMember |  |  |
Initial cost of Land | 14,432 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_LexingtonAvenuePropertyMember |  |  |
Initial cost of Building, Leaseholds and Leasehold improvements | 12,355 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_LexingtonAvenuePropertyMember |  |  |
Costs capitalized subsequent to acquisition | 426,691 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_LexingtonAvenuePropertyMember |  |  |
Carrying amount of Land | 27,497 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_LexingtonAvenuePropertyMember |  |  |
Carring amount of Building, Leaseholds and Leasehold improvements | 425,981 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_LexingtonAvenuePropertyMember |  |  |
Construction in progress | 0 alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_LexingtonAvenuePropertyMember |  |  |
Total | 453,478 us-gaap_RealEstateGrossAtCarryingValue / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_LexingtonAvenuePropertyMember |  |  |
Accumulated depreciation and amortization | 128,798 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_LexingtonAvenuePropertyMember |  |  |
Date of construction | 2003 |  |  |
Date acquired | 1992 |  |  |
Lexington Avenue Property [Member] | Maximum [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 39 years |  |  |
Lexington Avenue Property [Member] | Minimum [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 9 years |  |  |
Rego Park 1 Shopping [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 78,246 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark1ShoppingMember |  |  |
Initial cost of Land | 1,647 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark1ShoppingMember |  |  |
Initial cost of Building, Leaseholds and Leasehold improvements | 8,953 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark1ShoppingMember |  |  |
Costs capitalized subsequent to acquisition | 50,553 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark1ShoppingMember |  |  |
Carrying amount of Land | 1,647 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark1ShoppingMember |  |  |
Carring amount of Building, Leaseholds and Leasehold improvements | 59,370 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark1ShoppingMember |  |  |
Construction in progress | 136 alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark1ShoppingMember |  |  |
Total | 61,153 us-gaap_RealEstateGrossAtCarryingValue / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark1ShoppingMember |  |  |
Accumulated depreciation and amortization | 27,569 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark1ShoppingMember |  |  |
Date of construction | 1959 |  |  |
Date acquired | 1992 |  |  |
Rego Park 1 Shopping [Member] | Maximum [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 39 years |  |  |
Rego Park 1 Shopping [Member] | Minimum [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 3 years |  |  |
Rego Park 2 Residential Property [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2ResidentialPropertyMember |  |  |
Initial cost of Land | 0 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2ResidentialPropertyMember |  |  |
Initial cost of Building, Leaseholds and Leasehold improvements | 0 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2ResidentialPropertyMember |  |  |
Costs capitalized subsequent to acquisition | 73,327 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2ResidentialPropertyMember |  |  |
Carrying amount of Land | 0 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2ResidentialPropertyMember |  |  |
Carring amount of Building, Leaseholds and Leasehold improvements | 0 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2ResidentialPropertyMember |  |  |
Construction in progress | 73,327 alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2ResidentialPropertyMember |  |  |
Total | 73,327 us-gaap_RealEstateGrossAtCarryingValue / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2ResidentialPropertyMember |  |  |
Accumulated depreciation and amortization | 0 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2ResidentialPropertyMember |  |  |
Date acquired | 1992 |  |  |
Rego Park 2 Retail Property [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 266,534 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2RetailPropertyMember |  |  |
Initial cost of Land | 3,127 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2RetailPropertyMember |  |  |
Initial cost of Building, Leaseholds and Leasehold improvements | 1,467 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2RetailPropertyMember |  |  |
Costs capitalized subsequent to acquisition | 384,926 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2RetailPropertyMember |  |  |
Carrying amount of Land | 3,127 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2RetailPropertyMember |  |  |
Carring amount of Building, Leaseholds and Leasehold improvements | 386,260 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2RetailPropertyMember |  |  |
Construction in progress | 133 alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2RetailPropertyMember |  |  |
Total | 389,520 us-gaap_RealEstateGrossAtCarryingValue / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2RetailPropertyMember |  |  |
Accumulated depreciation and amortization | 52,747 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark2RetailPropertyMember |  |  |
Date of construction | 2009 |  |  |
Date acquired | 1992 |  |  |
Rego Park 2 Retail Property [Member] | Maximum [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 40 years |  |  |
Rego Park 2 Retail Property [Member] | Minimum [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 3 years |  |  |
Paramus Property [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 68,000 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_ParamusPropertyMember |  |  |
Initial cost of Land | 1,441 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_ParamusPropertyMember |  |  |
Initial cost of Building, Leaseholds and Leasehold improvements | 0 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_ParamusPropertyMember |  |  |
Costs capitalized subsequent to acquisition | 10,313 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_ParamusPropertyMember |  |  |
Carrying amount of Land | 11,754 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_ParamusPropertyMember |  |  |
Carring amount of Building, Leaseholds and Leasehold improvements | 0 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_ParamusPropertyMember |  |  |
Construction in progress | 0 alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_ParamusPropertyMember |  |  |
Total | 11,754 us-gaap_RealEstateGrossAtCarryingValue / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_ParamusPropertyMember |  |  |
Accumulated depreciation and amortization | 0 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_ParamusPropertyMember |  |  |
Date acquired | 1992 |  |  |
Flushing Property [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_FlushingPropertyMember |  |  |
Initial cost of Land | 0 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_FlushingPropertyMember |  |  |
Initial cost of Building, Leaseholds and Leasehold improvements | 1,660 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_FlushingPropertyMember |  |  |
Costs capitalized subsequent to acquisition | (107)us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_FlushingPropertyMember |  |  |
Carrying amount of Land | 0 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_FlushingPropertyMember |  |  |
Carring amount of Building, Leaseholds and Leasehold improvements | 1,553 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_FlushingPropertyMember |  |  |
Construction in progress | 0 alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_FlushingPropertyMember |  |  |
Total | 1,553 us-gaap_RealEstateGrossAtCarryingValue / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_FlushingPropertyMember |  |  |
Accumulated depreciation and amortization | 791 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_FlushingPropertyMember |  |  |
Date of construction | 1975 |  |  |
Date acquired | 1992 |  |  |
Rego Park 3 Property [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark3PropertyMember |  |  |
Initial cost of Land | 779 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark3PropertyMember |  |  |
Initial cost of Building, Leaseholds and Leasehold improvements | 0 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark3PropertyMember |  |  |
Costs capitalized subsequent to acquisition | 2,196 us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark3PropertyMember |  |  |
Carrying amount of Land | 779 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark3PropertyMember |  |  |
Carring amount of Building, Leaseholds and Leasehold improvements | 503 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark3PropertyMember |  |  |
Construction in progress | 1,693 alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark3PropertyMember |  |  |
Total | 2,975 us-gaap_RealEstateGrossAtCarryingValue / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark3PropertyMember |  |  |
Accumulated depreciation and amortization | 120 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_RegoPark3PropertyMember |  |  |
Date acquired | 1992 |  |  |
Rego Park 3 Property [Member] | Maximum [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 15 years |  |  |
Rego Park 3 Property [Member] | Minimum [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Property, Plant and Equipment, Useful Life | 5 years |  |  |
Other Properties [Member] |  |  |  |
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Encumbrances | 0 us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_OtherPropertiesMember |  |  |
Initial cost of Land | 167 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_OtherPropertiesMember |  |  |
Initial cost of Building, Leaseholds and Leasehold improvements | 1,804 us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_OtherPropertiesMember |  |  |
Costs capitalized subsequent to acquisition | (1,804)us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_OtherPropertiesMember |  |  |
Carrying amount of Land | 167 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_OtherPropertiesMember |  |  |
Carring amount of Building, Leaseholds and Leasehold improvements | 0 us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_OtherPropertiesMember |  |  |
Construction in progress | 0 alx_RealEstateAndAccumulatedDepreciationCarryingAmountOfDevelopmentAndConstructionInProgress / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_OtherPropertiesMember |  |  |
Total | 167 us-gaap_RealEstateGrossAtCarryingValue / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_OtherPropertiesMember |  |  |
Accumulated depreciation and amortization | $ 0 us-gaap_RealEstateAccumulatedDepreciation / us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis = alx_OtherPropertiesMember |  |  |
Date acquired | 1992 |  |  |

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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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- Definition Amount of accumulated depreciation pertaining to real estate investments for entities with a substantial portion of business acquiring and holding investment real estate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 970 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28.FN4) -URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 10 -Section S99 -Paragraph 6 -Subparagraph (SX 210.5-04.(c) Schedule III) -URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 28 -Article 12 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph c -Subparagraph Schedule III -Article 5 + Details
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- Definition Amount before accumulated depreciation of buildings and improvements for entities with a substantial portion of business acquiring and holding investment real estate. Excludes real estate not held as an investment or interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 970 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-28) -URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 10 -Section S99 -Paragraph 6 -Subparagraph (SX 210.5-04.(c) Schedule III) -URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 28 -Article 12 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph c -Subparagraph Schedule III -Article 5 + Details
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