Noncontrolling Interests on the Company's Consolidated Financial Statements - Preferred Unit Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units	$ (1,536)	$ (25,845)
SL Green Operating Partnership
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units	(1,536)	(25,845)
SL Green Operating Partnership | Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	283,285	300,427
Issuance of preferred units	0	1,000
Redemption of preferred units	(82,750)	(18,142)
Accrued dividends on preferred units	1,634	0
Balance at end of period	$ 202,169	$ 283,285