Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator
Less: distributed earnings allocated to participating securities									$ (552)	$ (471)	$ (634)
Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic									231,760	85,953	234,312
Add back: undistributed earnings allocated to participating securities									$ (552)	$ (471)	$ (634)
Denominator
Weighted average common shares outstanding (shares)									86,753,000	98,571,000	100,185,000
Diluted weighted average common stock outstanding (shares)									91,530,000	103,403,000	104,881,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,138,647	774,782	263,991
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ (64,658)	$ 93,006	$ 109,142	$ 107,038	$ 29,270	$ 40,681	$ 8,641	$ 11,827	$ 244,528	$ 90,419	$ 245,082
Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic									243,976	89,948	244,448
Add back: undistributed earnings allocated to participating securities									$ 552	$ 471	$ 634
Denominator
Weighted average common shares outstanding (shares)									91,315,000	103,127,000	104,508,000
Stock-based compensation plans (shares)									215,000	276,000	373,000
Diluted weighted average common stock outstanding (shares)									91,530,000	103,403,000	104,881,000
Common stock shares excluded from the diluted shares outstanding (shares)									1,138,647	774,782	263,991