Basis of Presentation (Policies)	6 Months Ended
Jun. 30, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	The accompanying consolidated financial statements are unaudited and include the accounts of Alexander’s and its consolidated subsidiaries. All adjustments (which include only normal recurring adjustments) necessary to present fairly the financial position, results of operations and changes in cash flows have been made. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted. These consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q of the Securities and Exchange Commission (“SEC”) and should be read in conjunction with the consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2024, as filed with the SEC. We have made estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. The results of operations for the three and six months ended June 30, 2025 are not necessarily indicative of the operating results for the full year.
Recently Issued Accounting Literature	In December 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (“ASU 2023-09”). ASU 2023-09 requires entities to disclose additional information with respect to the effective tax rate reconciliation and to disclose the disaggregation by jurisdiction of income tax expense and income taxes paid. ASU 2023-09 is effective for fiscal years beginning after December 15, 2024, with early adoption permitted. We are currently evaluating the impact of ASU 2023-09 on our consolidated financial statements. In November 2024, the FASB issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses (“ASU 2024-03”), and in January 2025, the FASB issued ASU 2025-01, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Clarifying the Effective Date (“ASU 2025-01”). ASU 2024-03 requires additional disclosure of the nature of expenses included in the income statement as well as disclosures about specific types of expenses included in the expense captions presented in the income statement. ASU 2024-03, as clarified by ASU 2025-01, is effective for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027, with early adoption permitted. We are currently evaluating the impact of these standards on our consolidated financial statements.
Stock-Based Compensation	We account for stock-based compensation in accordance with Accounting Standards Codification (“ASC”) Topic 718, Compensation – Stock Compensation (“ASC 718”). Our 2016 Omnibus Stock Plan (the “Plan”) provides for grants of incentive and non-qualified stock options, restricted stock, stock appreciation rights, deferred stock units (“DSUs”) and performance shares, as defined, to the directors, officers and employees of the Company and Vornado.
Fair Value Measurements	ASC Topic 820, Fair Value Measurement (“ASC 820”) defines fair value and establishes a framework for measuring fair value. ASC 820 establishes a fair value hierarchy that prioritizes observable and unobservable inputs used to measure fair value into three levels: Level 1 – quoted prices (unadjusted) in active markets that are accessible at the measurement date for assets or liabilities that are highly liquid and are actively traded in secondary markets; Level 2 – observable prices that are based on inputs not quoted in active markets, but corroborated by market data; and Level 3 – unobservable inputs that are used when little or no market data is available. The fair value hierarchy gives the highest priority to Level 1 inputs and the lowest priority to Level 3 inputs. In determining fair value, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible as well as consider counterparty credit risk in our assessment of fair value.

Basis of Presentation (Policies)

6 Months Ended

Jun. 30, 2025

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The accompanying consolidated financial statements are unaudited and include the accounts of Alexander’s and its consolidated subsidiaries. All adjustments (which include only normal recurring adjustments) necessary to present fairly the financial position, results of operations and changes in cash flows have been made. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted. These consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q of the Securities and Exchange Commission (“SEC”) and should be read in conjunction with the consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2024, as filed with the SEC.

We have made estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. The results of operations for the three and six months ended June 30, 2025 are not necessarily indicative of the operating results for the full year.

Recently Issued Accounting Literature

In December 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (“ASU 2023-09”). ASU 2023-09 requires entities to disclose additional information with respect to the effective tax rate reconciliation and to disclose the disaggregation by jurisdiction of income tax expense and income taxes paid. ASU 2023-09 is effective for fiscal years beginning after December 15, 2024, with early adoption permitted. We are currently evaluating the impact of ASU 2023-09 on our consolidated financial statements.

In November 2024, the FASB issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses (“ASU 2024-03”), and in January 2025, the FASB issued ASU 2025-01, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Clarifying the Effective Date (“ASU 2025-01”). ASU 2024-03 requires additional disclosure of the nature of expenses included in the income statement as well as disclosures about specific types of expenses included in the expense captions presented in the income statement. ASU 2024-03, as clarified by ASU 2025-01, is effective for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027, with early adoption permitted. We are currently evaluating the impact of these standards on our consolidated financial statements.

Stock-Based Compensation

We account for stock-based compensation in accordance with Accounting Standards Codification (“ASC”) Topic 718, Compensation – Stock Compensation (“ASC 718”). Our 2016 Omnibus Stock Plan (the “Plan”) provides for grants of incentive and non-qualified stock options, restricted stock, stock appreciation rights, deferred stock units (“DSUs”) and performance shares, as defined, to the directors, officers and employees of the Company and Vornado.

Fair Value Measurements

ASC Topic 820, Fair Value Measurement (“ASC 820”) defines fair value and establishes a framework for measuring fair value. ASC 820 establishes a fair value hierarchy that prioritizes observable and unobservable inputs used to measure fair value into three levels: Level 1 – quoted prices (unadjusted) in active markets that are accessible at the measurement date for assets or liabilities that are highly liquid and are actively traded in secondary markets; Level 2 – observable prices that are based on inputs not quoted in active markets, but corroborated by market data; and Level 3 – unobservable inputs that are used when little or no market data is available. The fair value hierarchy gives the highest priority to Level 1 inputs and the lowest priority to Level 3 inputs. In determining fair value, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible as well as consider counterparty credit risk in our assessment of fair value.