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Noncontrolling Interests on the Company's Consolidated Financial Statements - Additional Information (Details) | 3 Months Ended | 6 Months Ended | 12 Months Ended |  |  |  |  |  |
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Jun. 30, 2018 USD ($) shares $ / shares | Jun. 30, 2017 USD ($) | Jun. 30, 2018 USD ($) shares $ / shares | Jun. 30, 2017 USD ($) | Dec. 31, 2017 USD ($) shares | Jun. 30, 2016 shares | Aug. 31, 2015 shares | Jul. 31, 2015 shares | Jun. 30, 2015 shares | Feb. 28, 2015 shares | Aug. 31, 2014 shares
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Balance at beginning of period | $ |  |  | $ 461,954,000 |  |  |  |  |  |  |  |
Net income | $ | $ 5,586,000 | $ 419,000 | 10,858,000 | $ 895,000 |  |  |  |  |  |  |
Accumulated other comprehensive income allocation | $ | 245,000 | (100,000) | 864,000 | (299,000) |  |  |  |  |  |  |
Balance at end of period | $ | $ 486,610,000 |  | $ 486,610,000 |  | $ 461,954,000 |  |  |  |  |  |
Number of company common stock issued on conversion of Series B preferred units |  |  | 6.71348 |  |  |  |  |  |  |  |
SL Green Operating Partnership |  |  |  |  |  |  |  |  |  |  |
Organization |  |  |  |  |  |  |  |  |  |  |
Noncontrolling interest in the operating partnership (as a percent) | 5.20% |  | 5.20% |  | 4.58% |  |  |  |  |  |
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares) | shares | 4,699,872 |  | 4,699,872 |  | 4,452,979 |  |  |  |  |  |
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares | 4,699,872.000 |  | 4,699,872.000 |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Balance at beginning of period | $ |  |  | $ 461,954,000 | 473,882,000 | $ 473,882,000 |  |  |  |  |  |
Distributions | $ |  |  | (7,712,000) |  | (14,266,000) |  |  |  |  |  |
Issuance of common units | $ |  |  | 17,714,000 |  | 25,723,000 |  |  |  |  |  |
Redemption of common units | $ |  |  | (1,561,000) |  | (21,574,000) |  |  |  |  |  |
Net income | $ |  |  | 10,858,000 |  | 3,995,000 |  |  |  |  |  |
Accumulated other comprehensive income allocation | $ | $ 245,000 | $ (100,000) | 864,000 | $ (299,000) | (94,000) |  |  |  |  |  |
Fair value adjustment | $ |  |  | 4,493,000 |  | (5,712,000) |  |  |  |  |  |
Balance at end of period | $ | $ 486,610,000 |  | $ 486,610,000 |  | $ 461,954,000 |  |  |  |  |  |
SL Green Operating Partnership | Series G Preferred Units |  |  |  |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares | 1,902,000 |  | 1,902,000 |  |  |  |  |  |  |  |
Dividend rate preferred units (as a percent) |  |  | 4.50% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | 1.125 |  |  |  |  |  |  |  |
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ 88.50 |  | $ 88.50 |  |  |  |  |  |  |  |
Number of company common stock issue on redemption of operation partnership common units |  |  | 1 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series F Preferred Units |  |  |  |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares | 60 |  | 60 |  |  |  |  |  |  |  |
Mandatory liquidation preference (in dollars per share) | $ | $ 1,000.00 |  | $ 1,000.00 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series K Preferred Units |  |  |  |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  | 563,954
Dividend rate preferred units (as a percent) |  |  | 3.50% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | 0.875 |  |  |  |  |  |  |  |
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ 134.67 |  | $ 134.67 |  |  |  |  |  |  |  |
Preferred units, shares authorized (in shares) | shares | 700,000 |  | 700,000 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series L Preferred Units |  |  |  |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  | 378,634
Dividend rate preferred units (as a percent) |  |  | 4.00% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | $ 1.00 |  |  |  |  |  |  |  |
Preferred units, shares authorized (in shares) | shares | 500,000 |  | 500,000 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series M Preferred Units |  |  |  |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  |  |  |  |  | 1,600,000 |
Dividend rate preferred units (as a percent) |  |  | 3.75% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | $ 0.9375 |  |  |  |  |  |  |  |
Preferred units, shares authorized (in shares) | shares | 1,600,000 |  | 1,600,000 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series N Preferred Units |  |  |  |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  |  |  |  | 552,303 |  |
Dividend rate preferred units (as a percent) |  |  | 3.00% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | $ 0.75 |  |  |  |  |  |  |  |
Preferred units, shares authorized (in shares) | shares | 552,303 |  | 552,303 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series O Preferred Units |  |  |  |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Dividend rate preferred units (as a percent) |  |  | 6.25% |  |  |  |  |  |  |  |
Preferred units, shares authorized (in shares) | shares | 1 |  | 1 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series P Preferred Units |  |  |  |  |  |  |  |  |  |  |
Organization |  |  |  |  |  |  |  |  |  |  |
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares | 200,000 |  | 200,000 |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  |  |  | 200,000 |  |  |
Dividend rate preferred units (as a percent) |  |  | 4.00% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | $ 1.00 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series Q Preferred Units |  |  |  |  |  |  |  |  |  |  |
Organization |  |  |  |  |  |  |  |  |  |  |
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares | 268,000 |  | 268,000 |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  |  |  | 268,000 |  |  |
Dividend rate preferred units (as a percent) |  |  | 3.50% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | 0.875 |  |  |  |  |  |  |  |
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ 148.95 |  | $ 148.95 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series R Preferred Units |  |  |  |  |  |  |  |  |  |  |
Organization |  |  |  |  |  |  |  |  |  |  |
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares | 400,000 |  | 400,000 |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  |  | 400,000 |  |  |  |
Dividend rate preferred units (as a percent) |  |  | 3.50% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | 0.875 |  |  |  |  |  |  |  |
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ 154.89 |  | $ 154.89 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series S Preferred Units |  |  |  |  |  |  |  |  |  |  |
Organization |  |  |  |  |  |  |  |  |  |  |
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares | 1,077,280 |  | 1,077,280 |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  |  | 1,077,280 |  |  |  |
Dividend rate preferred units (as a percent) |  |  | 4.00% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | $ 1.00 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series T Preferred Units |  |  |  |  |  |  |  |  |  |  |
Organization |  |  |  |  |  |  |  |  |  |  |
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares | 230,000 |  | 230,000 |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  | 230,000 |  |  |  |  |
Dividend rate preferred units (as a percent) |  |  | 2.75% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | 0.6875 |  |  |  |  |  |  |  |
Operating partnership common stock value use for conversion of preferred units (in dollars per share) | $ 119.02 |  | $ 119.02 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series U Preferred Units |  |  |  |  |  |  |  |  |  |  |
Organization |  |  |  |  |  |  |  |  |  |  |
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares | 680,000 |  | 680,000 |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  | 680,000 |  |  |  |  |
Dividend rate preferred units (as a percent) |  |  | 4.50% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 25.00 |  | $ 25.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | 1.125 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series U Preferred Units | Minimum |  |  |  |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | $ 0.75 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series A Preferred Units |  |  |  |  |  |  |  |  |  |  |
Organization |  |  |  |  |  |  |  |  |  |  |
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares) | shares | 109,161 |  | 109,161 |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares |  |  |  |  |  |  | 109,161 |  |  |  |
Dividend rate preferred units (as a percent) |  |  | 3.50% |  |  |  |  |  |  |  |
Liquidation preference of preferred units (in dollars per share) | $ 1,000.00 |  | $ 1,000.00 |  |  |  |  |  |  |  |
Annual dividends on preferred units (in dollars per share) |  |  | $ 35.00 |  |  |  |  |  |  |  |
SL Green Operating Partnership | Series B Preferred Units |  |  |  |  |  |  |  |  |  |  |
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership |  |  |  |  |  |  |  |  |  |  |
Number of preferred units issued (in shares) | shares | 0 |  | 0 |  |  |  |  |  |  |  |

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- Definition The aggregate liquidation preference (or restrictions) of stock classified as temporary equity that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.28(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The per share liquidation preference (or restrictions) of stock classified as temporary equity that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.28(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The number of securities classified as temporary equity that have been sold (or granted) to the entity's shareholders. Securities issued include securities outstanding and securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(27)(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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