Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Denominator
Weighted average common shares outstanding (shares)	97,783,000	100,233,000	99,431,000	100,140,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,175,708	673,298	1,076,695	753,344
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 40,681	$ 35,915	$ 61,149	$ 199,101
Denominator
Weighted average common shares outstanding (shares)	102,326,000	104,730,000	104,001,000	104,412,000
Stock-based compensation plans (shares)	244,000	413,000	279,000	349,000
Diluted weighted average common units outstanding (shares)	102,570,000	105,143,000	104,280,000	104,761,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,175,708	673,298	1,076,695	753,344