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Partners' Capital of the Operating Partnership - Additional Information (Details) | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2018 shares | Jun. 30, 2018 shares | Dec. 31, 2017 shares | Sep. 30, 2017 shares | Jun. 30, 2017 shares | Dec. 31, 2016 shares
Common Stock |  |  |  |  |  |
Stockholders' Equity |  |  |  |  |  |
Units outstanding (units) | 85,594,000 | 85,725,000 | 92,803,000 | 97,446,000 | 98,367,000 | 100,562,000
SL Green Operating Partnership |  |  |  |  |  |
Stockholders' Equity |  |  |  |  |  |
Noncontrolling interest in the operating partnership (as a percent) | 5.10% |  | 4.58% |  |  |
Number of units of operating partnership owned by the noncontrolling interest unit holders (units) | 4,600,521 |  | 4,452,979 |  |  |
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) | 85,593,863 |  |  |  |  |

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