Noncontrolling Interests on the Company's Consolidated Financial Statements - Preferred Unit Activity (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Rollforward Analysis of Preferred Unit Activity
Redemption of preferred units	$ (20,650)
SL Green Operating Partnership
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units	27,898	$ 56,469
Redemption of preferred units	(41,605)	(31,653)
SL Green Operating Partnership | Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	71,115	49,550
Issuance of preferred units	211,601	23,565
Redemption of preferred units	(200)	(2,000)
Balance at end of period	$ 282,516	$ 71,115