Noncontrolling Interests on the Company's Consolidated Financial Statements (Common Unit Activity) (Details) - SL Green Operating Partnership - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units	$ 20,824	$ 78,495
Redemption of preferred units	(13,242)	(31,805)
Preferred Units
Rollforward Analysis of Preferred Unit Activity
Balance at beginning of period	302,010	282,516
Issuance of preferred units	0	22,793
Redemption of preferred units	(125)	(3,299)
Balance at end of period	$ 301,885	$ 302,010