Noncontrolling Interests on the Company's Consolidated Financial Statements - Common Unit Activity (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units		$ (1,536)
SL Green Operating Partnership
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units		(1,536)
SL Green Operating Partnership | Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	$ 202,169	$ 283,285	$ 283,285
Issuance of preferred units	0		0
Redemption of preferred units	(3,631)		(82,750)
Dividends paid on preferred units	(1,731)		(6,163)
Accrued dividends on preferred units	1,696		7,797
Balance at end of period	$ 198,503		$ 202,169