Stockholders' Equity of the Company (Earnings per Share)(Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic Earnings:
Income attributable to SL Green common stockholders	$ 34,252	$ 163,658	$ 190,930	$ 167,829
Diluted Earnings:
Income attributable to SL Green common stockholders	$ 35,915	$ 170,125	$ 199,101	$ 174,463
Basic Shares:
Weighted average common shares outstanding (shares)	100,233,000	99,621,000	100,140,000	99,205,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	4,497,000	3,901,000	4,272,000	3,924,000
Stock-based compensation plans (shares)	413,000	407,000	349,000	480,000
Diluted weighted average common stock outstanding (shares)	105,143,000	103,929,000	104,761,000	103,609,000
Common stock shares excluded from the diluted shares outstanding (shares)	673,298	263,236	753,344	231,970
Common Stock
Effect of Dilutive Securities:
Redemption of units to common shares	$ 1,663	$ 6,467	$ 8,171	$ 6,634