Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic Earnings:
Income attributable to SL Green common stockholders	$ 38,869	$ 34,252	$ 58,442	$ 190,930
Diluted Earnings:
Income attributable to SL Green common stockholders	$ 40,681	$ 35,915	$ 61,149	$ 199,101
Basic Shares:
Weighted average common shares outstanding (shares)	97,783,000	100,233,000	99,431,000	100,140,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	4,543,000	4,497,000	4,570,000	4,272,000
Stock-based compensation plans (shares)	244,000	413,000	279,000	349,000
Diluted weighted average common stock outstanding (shares)	102,570,000	105,143,000	104,280,000	104,761,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,175,708	673,298	1,076,695	753,344
Common Stock
Effect of Dilutive Securities:
Redemption of units to common shares	$ 1,812	$ 1,663	$ 2,707	$ 8,171