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v3.23.1

Commitments and Contingencies (Details) | 3 Months Ended
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Mar. 31, 2023 USD ($)
Loss Contingencies [Line Items] |
Standby letters of credit, outstanding | $ 900,000
All Risk Property and Rental Value |
Loss Contingencies [Line Items] |
Insurance maximum coverage per incident | 1,700,000,000
Terrorism Coverage Including NBCR |
Loss Contingencies [Line Items] |
Insurance maximum coverage per incident | 1,700,000,000
Insurance maximum coverage in aggregate | $ 1,700,000,000
NBCR |
Loss Contingencies [Line Items] |
Federal government responsibility (in percentage) | 80.00%
NBCR | FNSIC |
Loss Contingencies [Line Items] |
Insurance deductible | $ 298,000
Self insured responsibility (in percentage) | 20.00%
General Liability |
Loss Contingencies [Line Items] |
Insurance maximum coverage per property | $ 300,000,000
Insurance maximum coverage per incident | 300,000,000
Disease Coverage |
Loss Contingencies [Line Items] |
Insurance maximum coverage per incident | $ 30,000,000

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
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Namespace Prefix: | alx_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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
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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
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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
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Namespace Prefix: | alx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |