Noncontrolling Interests on the Company's Consolidated Financial Statements - Common Unit Activity (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units	$ (54)	$ (25,791)
SL Green Operating Partnership
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units			$ 16,493	$ 23,655
Redemption of preferred units	(54)	(25,791)	(16,388)	(60,718)
SL Green Operating Partnership | Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period		$ 300,427	300,427	301,735
Issuance of preferred units			1,000	0
Redemption of preferred units			(15,142)	(1,308)
Balance at end of period	$ 286,285		$ 286,285	$ 300,427