Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Denominator
Weighted average common shares outstanding (shares)	87,176,000	99,900,000	88,772,000	100,268,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,158,317		1,184,735
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 109,142	$ 8,641	$ 216,180	$ 20,468
Denominator
Weighted average common shares outstanding (shares)	91,882,000	104,462,000	93,467,000	104,852,000
Stock-based compensation plans (shares)	201,000	270,000	200,000	288,000
Diluted weighted average common units outstanding (shares)	92,083,000	104,732,000	93,667,000	105,140,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,158,317	986,390	1,184,735	979,676