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Significant accounting policies (Tables) | 12 Months Ended
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Dec. 31, 2012
Accounting Policies [Abstract] |
Reconciliation Of Net Income Attributable To Common Stockholders To Estimated Taxable Income [Table Text Block] |
| (Unaudited and in thousands) | Years Ended December 31, |  |
|  |  | 2012 |  | 2011 |  | 2010 |  |
| Net income attributable to Alexander’s | $ | 674,387 |  | $ | 79,423 |  | $ | 66,429 |  |
| Additional tax gain on sale of the Kings Plaza Regional |  |  |  |  |  |  |  |  |  |
|  | Shopping Center |  | 23,928 |  |  | - |  |  | - |  |
| Straight-line rent adjustments |  | (4,475) |  |  | (12,609) |  |  | (15,182) |  |
| Depreciation and amortization timing differences |  | 910 |  |  | 1,263 |  |  | 602 |  |
| Interest expense |  | 29 |  |  | (2,425) |  |  | - |  |
| Reversal of liability for income taxes |  | - |  |  | - |  |  | (3,162) |  |
| Other |  | 4,396 |  |  | (3,429) |  |  | 6,245 |  |
| Taxable income before net operating loss ("NOL") |  | 699,175 |  |  | 62,223 |  |  | 54,932 |  |
| NOL carried forward |  | - |  |  | - |  |  | (16,939) |  |
| Estimated taxable income | $ | 699,175 |  | $ | 62,223 |  | $ | 37,993 |  |

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- Definition Table reconciling net income attributable to common stockholders to estimated taxable income + References No definition available. + Details
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- Details
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