Noncontrolling Interests on the Company's Consolidated Financial Statements (Common Unit Activity) (Details) - SL Green Operating Partnership - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units	$ 75,352	$ 30,506
Redemption of preferred units	(12,746)	(55,697)
Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	282,516	71,115
Issuance of preferred units	22,793	211,601
Redemption of preferred units	(2,999)	(200)
Balance at end of period	$ 302,310	$ 282,516