| Cover | 12 Months Ended |
| Dec. 31, 2022 | |
| Document Information [Line Items] | |
| Document Type | DEF 14A |
| Amendment Flag | false |
| Entity Information [Line Items] | |
| Entity Registrant Name | ALEXANDER’S, INC. |
| Entity Central Index Key | 0000003499 |
| Pay vs Performance Disclosure - USD ($) | 12 Months Ended | ||
| Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | |
| Pay vs Performance Disclosure [Table] | |||
| Pay vs Performance [Table Text Block] | Pay Versus Performance As required by Section 953(a) of the Dodd-Frank Wall Street Reform and Consumer Protection Act, and Item 402(v) of Regulation S-K, defined Year (a) Summary ($) (b) Compensation ($) (c) Average Summary Non-PEO (d) Average Non-PEO (d) Value of Initial Fixed $100 Net Income ($) (g) Total ($) (e) Peer Group Total ($) (f) 2022 175,188 175,188 — — 75.21 124.22 57,632,000 2021 169,698 169,698 — — 82.73 165.51 132,930,000 2020 164,181 164,181 — — 82.45 117.14 41,939,000 (a) Per Item 402(v) if Regulation S-K, (b) Reflects compensation amounts reported in the “Summary Compensation Table” for our Chief Executive Officer, Steven Roth, for the respective years shown. (c) In accordance with Item 402(v), there was no additional compensation amounts paid to our Chief Executive Officer, Steven Roth for the respective time periods other than what is noted in column b (“Summary Compensation Table Total for PEO”) and there are no adjustments that are applicable to the Summary Compensation Table Total for PEO in order to calculate compensation actually paid as all stock awards made to Mr. Roth were fully vested at grant (and, accordingly, the grant date fair value of the awards used for purposes of the Summary Compensation Table is the same grant date fair value as is used for purposes of calculating compensation actually paid). (d) Reflects compensation amounts reported in the “Summary Compensation Table” and paid to Gary Hansen, Chief Financial Officer, since November 2, 2021 and Matthew Iocco, previous Chief Financial Officer, for the remaining time period. There was no compensation paid to Non-PEO (e) Represents the cumulative total shareholder return of Alexander’s, Inc. for the respective measurement period, calculated based on a fixed investment of $100 measured from the market close on December 31, 2019 (the last trading day of 2019) through and including the end of the fiscal year for each fiscal year reported in the table. (f) Represents the cumulative total shareholder return of the National Association of Real Estate Investment Trusts (“NAREIT”) All Equity Index (which we also use for purposes of the stock performance graph required by Item 201(k) of Regulation S-K) (g) Reflects “Net Income” in the Company’s Consolidated Statements of Income included in the Company’s Annual Reports on Form 10-K. In determining compensation actually paid for 2022, we did not consider any financial performance measures due to the fact the Company’s PEO’s sole compensation relates to compensation received in his capacity as a director which is based on market rates for board of director fees, taking into account the value of a director’s time. Accordingly, we have not included a tabular list of our most important financial performance measures to determine Fiscal 2022 compensation actually paid pursuant to Item 402(v) of Regulation S-K | ||
| Named Executive Officers, Footnote [Text Block] | Reflects compensation amounts reported in the “Summary Compensation Table” and paid to Gary Hansen, Chief Financial Officer, since November 2, 2021 and Matthew Iocco, previous Chief Financial Officer, for the remaining time period. | ||
| Peer Group Issuers, Footnote [Text Block] | Represents the cumulative total shareholder return of the National Association of Real Estate Investment Trusts (“NAREIT”) All Equity Index (which we also use for purposes of the stock performance graph required by Item 201(k) of Regulation S-K) | ||
| PEO Total Compensation Amount | $ 175,188 | $ 169,698 | $ 164,181 |
| PEO Actually Paid Compensation Amount | $ 175,188 | 169,698 | 164,181 |
| Adjustment To PEO Compensation, Footnote [Text Block] | In accordance with Item 402(v), there was no additional compensation amounts paid to our Chief Executive Officer, Steven Roth for the respective time periods other than what is noted in column b (“Summary Compensation Table Total for PEO”) and there are no adjustments that are applicable to the Summary Compensation Table Total for PEO in order to calculate compensation actually paid as all stock awards made to Mr. Roth were fully vested at grant (and, accordingly, the grant date fair value of the awards used for purposes of the Summary Compensation Table is the same grant date fair value as is used for purposes of calculating compensation actually paid). | ||
| Non-PEO NEO Average Total Compensation Amount | $ 0 | 0 | 0 |
| Non-PEO NEO Average Compensation Actually Paid Amount | $ 0 | 0 | 0 |
| Adjustment to Non-PEO NEO Compensation Footnote [Text Block] | There was no compensation paid to Non-PEO | ||
| Compensation Actually Paid vs. Total Shareholder Return [Text Block] | Compensation Actually Paid vs TSR and Group TSR | ||
| Compensation Actually Paid vs. Net Income [Text Block] | Compensation | ||
| Total Shareholder Return Vs Peer Group [Text Block] | Compensation Actually Paid vs TSR and Group TSR | ||
| Total Shareholder Return Amount | $ 75.21 | 82.73 | 82.45 |
| Peer Group Total Shareholder Return Amount | 124.22 | 165.51 | 117.14 |
| Net Income (Loss) | $ 57,632,000 | $ 132,930,000 | $ 41,939,000 |
| PEO Name | Steven Roth | ||
