Noncontrolling Interests on the Company's Consolidated Financial Statements - Common Unit Activity (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended	12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period		$ 283,285		$ 283,285
Redemption of preferred units	$ 0	(1,536)	$ (25,791)
Balance at end of period	225,448			225,448	$ 283,285
SL Green Operating Partnership
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period		283,285		283,285
Redemption of preferred units	0	(1,536)	$ (25,791)
Balance at end of period	225,448			225,448	283,285
SL Green Operating Partnership | Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period		$ 283,285		283,285	300,427
Issuance of preferred units				0	1,000
Redemption of preferred units				(59,800)	(18,142)
Accrued dividends on preferred units				1,963	0
Balance at end of period	$ 225,448			$ 225,448	$ 283,285