Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Denominator
Weighted average common shares outstanding (shares)	90,520,000	100,643,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,210,802	1,025,419
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 107,038	$ 11,827
Denominator
Weighted average common shares outstanding (shares)	95,203,000	105,250,000
Stock-based compensation plans (shares)	53,000	304,000
Diluted weighted average common units outstanding (shares)	95,256,000	105,554,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,210,802	1,025,419