Noncontrolling Interests on the Company's Consolidated Financial Statements - Preferred Unit Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units	$ (25,845)
SL Green Operating Partnership
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units	19,403	$ 23,655
Redemption of preferred units	(27,962)	(60,718)
SL Green Operating Partnership | Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	300,427	301,735
Issuance of preferred units	1,000	0
Redemption of preferred units	(18,142)	(1,308)
Balance at end of period	$ 283,285	$ 300,427