Partners' Capital of the Operating Partnership (EPS) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stockholders' Equity
Weighted average common shares outstanding (shares)	99,900,000	100,134,000	100,268,000	100,093,000
Common stock shares excluded from the diluted shares outstanding (shares)	986,390	739,636	979,676	845,026
SL Green Operating Partnership
Stockholders' Equity
Net income attributable to SLGOP common unitholders	$ 8,641	$ 139,043	$ 20,468	$ 163,186
Weighted average common shares outstanding (shares)	104,462,000	104,476,000	104,852,000	104,251,000
Stock-based compensation plans (shares)	270,000	316,000	288,000	282,000
Diluted weighted average common units outstanding (shares)	104,732,000	104,792,000	105,140,000	104,533,000
Common stock shares excluded from the diluted shares outstanding (shares)	986,390	739,636	979,676	845,026