XML 58 R46.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Commitments and Contingencies - Additional Information (Detail) ft² in Thousands | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2016 USD ($) | Feb. 28, 2014 fire | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Sep. 30, 2018 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2021 USD ($) | Oct. 03, 2018 | Dec. 31, 2017 USD ($) | Apr. 04, 2017 ft² | Dec. 31, 2001 a
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Insurance maximum coverage per occurrence |  |  |  |  | $ 300,000,000 |  |  |  |  |  |
Insurance maximum coverage per property |  |  |  |  | 300,000,000 |  |  |  |  |  |
Mortgages payable, net of deferred debt issuance costs |  |  | $ 1,162,928,000 |  | 1,162,928,000 |  |  |  | $ 1,240,222,000 |  |
Annual property rental |  |  | 38,250,000 | $ 37,970,000 | 115,109,000 | $ 114,507,000 |  |  |  |  |
Deferred leasing cost, net |  |  | 41,792,000 |  | 41,792,000 |  |  |  | $ 45,790,000 |  |
Standby letters of credit, outstanding |  |  | 1,040,000 |  | 1,040,000 |  |  |  |  |  |
Rego Park I | Sears |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of fires | fire |  | 2 |  |  |  |  |  |  |  |  |
Area of property | ft² |  |  |  |  |  |  |  |  |  | 195 |
Annual property rental |  |  |  |  | 10,300,000 |  |  |  |  |  |
Straight line rent receivable |  |  | 2,973,000 |  |  |  |  |  |  |  |
Deferred leasing cost, net |  |  | $ 312,000 |  | 312,000 |  |  |  |  |  |
Rego Park I | Sears | Minimum |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value |  |  |  |  | $ 4,000,000 |  |  |  |  |  |
Paramus | IKEA | Tenant Occupant |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Area of land | a |  |  |  |  |  |  |  |  |  |  | 30.3
Fixed interest rate on the debt |  |  | 2.90% |  | 2.90% |  |  |  |  |  |
Triple-net rent, annual amount |  |  |  |  | $ 700,000 |  |  |  |  |  |
Mortgages payable, net of deferred debt issuance costs |  |  | $ 68,000,000 |  | $ 68,000,000 |  |  |  |  |  |
Debt instrument maturity date |  |  |  |  | Oct. 04, 2021 |  |  |  |  |  |
All Risk Property and Rental Value |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Insurance maximum coverage per occurrence |  |  |  |  | $ 1,700,000,000 |  |  |  |  |  |
Terrorism Coverage Including NBCR |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Insurance maximum coverage per occurrence |  |  |  |  | 1,700,000,000 |  |  |  |  |  |
Insurance maximum coverage in aggregate |  |  |  |  | $ 1,700,000,000 |  |  |  |  |  |
NBCR |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Insurance coverage end date |  |  |  |  | Dec. 01, 2020 |  |  |  |  |  |
Self insured responsibility |  |  | 18.00% |  | 18.00% |  |  |  |  |  |
Federal government responsibility |  |  | 82.00% |  | 82.00% |  |  |  |  |  |
NBCR | FNSIC |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Insurance deductible |  |  |  |  | $ 306,000 |  |  |  |  |  |
Forecast | Paramus | IKEA | Tenant Occupant |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Lease purchase option amount |  |  |  |  |  |  | $ 75,000,000 |  |  |  |
Purchase option not exercised amount included in triple net rent over remainder of lease |  |  |  |  |  |  | 68,000,000 |  |  |  |
Purchase option exercised, net cash proceeds from sale of land |  |  |  |  |  |  | 7,000,000 |  |  |  |
Purchase option exercised, gain on sale of land |  |  |  |  |  |  | $ 60,000,000 |  |  |  |
Lease term range as Lessor |  |  |  |  |  |  | 20 years |  |  |  |
Loan amortization period |  |  |  |  |  |  | 20 years |  |  |  |
Estimated Future Damages | Rego Park I | Sears |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value | $ 650,000 |  |  |  |  |  |  |  |  |  |
Estimated Future Damages | Rego Park I | Sears | Minimum |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Loss contingency, damages sought, value |  |  |  |  | 25,000,000 |  |  |  |  |  |
Estimated Future Damages | Rego Park I | Sears | Maximum |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Reasonably possible losses |  |  | $ 650,000 |  | $ 650,000 |  |  |  |  |  |
Subsequent Event | Paramus | IKEA | Tenant Occupant |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fixed interest rate on the debt |  |  |  |  |  |  |  | 4.72% |  |  |

X
- Definition The percentage of the covered portion of a loss above the deductible for which the Federal Government is responsible for covered losses. + References No definition available. + Details
Name: | alx_FederalGovernmentResponsibility
Namespace Prefix: | alx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Insurance coverage end date. + References No definition available. + Details
Name: | alx_InsuranceCoverageEndDate
Namespace Prefix: | alx_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition The deductible owed by our wholly owned insurance subsidiary in the event of a covered loss. + References No definition available. + Details
Name: | alx_InsuranceDeductible
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Insurance maximum coverage limit in aggregate. + References No definition available. + Details
Name: | alx_InsuranceMaximumCoverageInAggregate
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Insurance maximum coverage limit per incident. + References No definition available. + Details
Name: | alx_InsuranceMaximumCoveragePerIncident
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Insurance Maximum Coverage Per Property. + References No definition available. + Details
Name: | alx_InsuranceMaximumCoveragePerProperty
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Approximate rental term range for all outstanding leases to tenants in retail centers and office buildings. + References No definition available. + Details
Name: | alx_LeasesOfLessorRentalTermRange
Namespace Prefix: | alx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition In the event the tenant does not exercise its purchase option, the period over which the tenant's debt service portion of its rent must be sufficient to fully amortize the loan on the property + References No definition available. + Details
Name: | alx_LoanAmortizationPeriod
Namespace Prefix: | alx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of fires. + References No definition available. + Details
Name: | alx_NumberOfFires
Namespace Prefix: | alx_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Lease with purchase option to be exercised by lessee. + References No definition available. + Details
Name: | alx_PropertyPurchaseOptionExercisableByLessee
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The cash inflow from the sale of land held for use in case the purchase option is exercised by lessee. + References No definition available. + Details
Name: | alx_PurchaseOptionExercisedProceedsFromSaleOfLandHeldForUse
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount to be amortized over the remainder of the lease term if the purchase option is not exercised. + References No definition available. + Details
Name: | alx_PurchaseOptionNotExercisedAmountIncludedInTripleNetRentOverRemainderOfLease
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The percentage of the covered portion of a loss above the deductible for which our wholly owned insurance subsidiary is responsible for covered losses. + References No definition available. + Details
Name: | alx_SelfInsuredResponsibility
Namespace Prefix: | alx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Triple-net rent, annual amount + References No definition available. + Details
Name: | alx_TripleNetRentAnnualAmount
Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Area of land held. + References No definition available. + Details
Name: | us-gaap_AreaOfLand
Namespace Prefix: | us-gaap_
Data Type: | num:areaItemType
Balance Type: | na
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 Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(2)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
Name: | us-gaap_DebtInstrumentMaturityDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction. This element is net of accumulated amortization. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 25 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=77902619&loc=d3e40246-112709 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 25 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=77902619&loc=d3e40588-112709 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 35 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=77913719&loc=d3e40879-112712 + Details
Name: | us-gaap_DeferredCostsLeasingNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of difference between the carrying amount and the sales price of real estate properties sold as part of discontinued operations. + References No definition available. + Details
Name: | us-gaap_GainLossOnDispositionOfRealEstateDiscontinuedOperations
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The value (monetary amount) of the award the plaintiff seeks in the legal matter. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349 + Details
Name: | us-gaap_LossContingencyDamagesSoughtValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Reflects the estimated amount of loss from the specified contingency as of the balance sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=115931803&loc=d3e12021-110248 + Details
Name: | us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_NotesPayable
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=77902458&loc=d3e39896-112707 + Details
Name: | us-gaap_OperatingLeasesIncomeStatementLeaseRevenue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of the adjustment to rental revenues to measure escalating leasing revenues on a straight line basis. + References No definition available. + Details
Name: | us-gaap_StraightLineRentAdjustments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=alx_RegoPark1PropertyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | alx_RealEstatePropertyOccupantAxis=alx_SearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=alx_ParamusPropertyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | alx_RealEstatePropertyOccupantAxis=alx_IkeaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=alx_TenantOccupantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis=alx_AllRiskPropertyAndRentalValueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis=alx_TerrorismCoverageIncludingNbcrMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | alx_ScheduleOfInsuranceTypeAndTierIdentifierAxis=alx_NbcrMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=alx_FiftyNinthStreetInsuranceCompanyLlcMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=alx_EstimatedFutureDamagesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |