Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands		1 Months Ended		12 Months Ended
		Feb. 22, 2018	Nov. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly distributions declared, per share/unit (usd per share/unit)				$ 0.885	$ 0.85	$ 0.8125
Deconsolidation of a subsidiary	[1]			$ 395	$ 298,404	$ 695,204
SL Green Operating Partnership
Quarterly distributions declared, per share/unit (usd per share/unit)				$ 0.85	$ 0.8125	$ 0.775
Deconsolidation of a subsidiary	[2]			$ 395	$ 298,404	$ 695,204
Allianz Real Estate | 1515 Broadway
Deconsolidation of a subsidiary			$ 366,600
Ownership percentage in disposed asset		12.87%	30.13%
Allianz Real Estate | 1515 Broadway | SL Green Operating Partnership
Deconsolidation of a subsidiary			$ 366,600
Ownership percentage in disposed asset		12.87%	30.13%

[1] $366.6 million of the 2017 amount relates to 1515 Broadway. In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018. See Note 6, "Investments in Unconsolidated Joint Ventures.".

[2] $366.6 million of the 2017 amount relates to 1515 Broadway. In November 2017, the Company sold a 30.13% interest in 1515 Broadway to affiliates of Allianz Real Estate. The sale did not meet the criteria for sale accounting and as a result the property was accounted for under the profit sharing method. The Company achieved sale accounting upon adoption of ASC 610-20 in January 2018 and closed on the sale of an additional 12.87% interest in the property to Allianz in February 2018.