Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator
Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic	$ 33,049	$ 88,051	$ 237,686	$ 293,022
Add back: distributed earnings allocated to participating securities	108	125	325	371
Add back: undistributed earnings allocated to participating securities	0	33	41	138
Income attributable to SL Green common stockholders	$ 34,876	$ 93,006	$ 250,358	$ 309,187
Denominator
Weighted average common shares outstanding (shares)	82,292,000	85,566,000	82,855,000	87,692,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,317,803	941,636
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 34,876	$ 93,006	$ 250,358	$ 309,187
Less: distributed earnings allocated to participating securities	(108)	(125)	(325)	(371)
Less: undistributed earnings allocated to participating securities	0	(33)	(41)	(138)
Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic	34,768	92,848	249,992	308,678
Add back: distributed earnings allocated to participating securities	108	125	325	371
Add back: undistributed earnings allocated to participating securities	0	33	41	138
Income attributable to SL Green common stockholders	$ 34,876	$ 93,006	$ 250,358	$ 309,187
Denominator
Basic weighted average common units outstanding (in shares)	86,550,000	90,209,000	87,138,000	92,369,000
Stock-based compensation plans (shares)	164,000	219,000	171,000	211,000
Diluted weighted average common units outstanding (shares)	86,714,000	90,428,000	87,309,000	92,580,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,317,803	941,636	1,266,296	1,137,971