XML 60 R45.htm IDEA: XBRL DOCUMENT
v3.24.0.1

Marketable Securities (Details) $ in Thousands | 1 Months Ended
--- | ---
Dec. 31, 2021 USD ($) shares
Marketable Securities [Abstract] |
Number of shares sold (shares) | shares | 564,612
Cash proceeds | $ | $ 9,506

X
- Definition Number of Shares Sold + References No definition available. + Details
Name: | alx_NumberOfSharesSold
Namespace Prefix: | alx_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_MarketableSecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of cash inflow from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as investing activity. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 19 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-19 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 45 -Paragraph 1 -SubTopic 10 -Topic 321 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479567/321-10-45-1 + Details
Name: | us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration