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Partners' Capital of the Operating Partnership - Additional Information (Details) - shares | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2021 | Jun. 30, 2021 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Dec. 31, 2019
Common Stock |  |  |  |  |  |
Stockholders' Equity |  |  |  |  |  |
Units outstanding (units) | 66,865,000 | 67,880,000 | 68,508,000 | 70,969,000 | 71,586,000 | 76,956,000
SL Green Operating Partnership |  |  |  |  |  |
Stockholders' Equity |  |  |  |  |  |
Number of units of operating partnership owned by the noncontrolling interest unit holders (units) | 3,888,034 |  | 3,938,823 |  |  |
SL Green Operating Partnership | Series I Preferred Units |  |  |  |  |  |
Stockholders' Equity |  |  |  |  |  |
Units outstanding (units) | 9,200,000 |  |  |  |  |
Period of restriction to redeem OP Units | 1 year |  |  |  |  |
Conversion of stock, shares issued | 1 |  |  |  |  |
SL Green Operating Partnership | Common Stock |  |  |  |  |  |
Stockholders' Equity |  |  |  |  |  |
Units outstanding (units) | 66,865,416 |  |  |  |  |

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