Noncontrolling Interests on the Company's Consolidated Financial Statements (Common Unit Activity) (Details) - SL Green Operating Partnership $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares
Preferred Units [Line Items]
Noncontrolling interest in the operating partnership (as a percent)	4.33%	4.16%
Rollforward Analysis of Preferred Unit Activity
Issuance of preferred units	$ 18,240	$ 78,495
Redemption of preferred units	$ (13,112)	$ (31,805)
Number of units of operating partnership owned by the noncontrolling interest unit holders (units) | shares	4,562,717	4,363,716
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	0	(3,299)
Balance at end of period	$ 302,010	$ 302,010