Stockholders' Equity of the Company (Earnings per Share)(Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic Earnings:
Income attributable to SL Green common stockholders	$ 8,222	$ 133,457	$ 19,573	$ 156,678
Diluted Earnings:
Income attributable to SL Green common stockholders	$ 8,641	$ 139,043	$ 20,468	$ 163,186
Basic Shares:
Weighted average common shares outstanding (shares)	99,900,000	100,134,000	100,268,000	100,093,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	4,562,000	4,342,000	4,584,000	4,158,000
Stock-based compensation plans (shares)	270,000	316,000	288,000	282,000
Diluted weighted average common stock 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
Common Stock
Effect of Dilutive Securities:
Redemption of units to common shares	$ 419	$ 5,586	$ 895	$ 6,508