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Equity (Details 5) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 3.00% Senior unsecured notes maturing on October 15, 2017	Jun. 30, 2011 3.00% Senior unsecured notes maturing on October 15, 2017	Dec. 31, 2010 3.00% Senior unsecured notes maturing on October 15, 2017	Jun. 30, 2011 3.00% Senior unsecured notes maturing on March 30, 2027	Jun. 30, 2011 3.00% Senior unsecured notes maturing on March 30, 2027	Dec. 31, 2010 3.00% Senior unsecured notes maturing on March 30, 2027	Jun. 30, 2011 4.00% Senior unsecured notes maturing on June 15, 2025	Jun. 30, 2011 4.00% Senior unsecured notes maturing on June 15, 2025	Dec. 31, 2010 4.00% Senior unsecured notes maturing on June 15, 2025
Basic Earnings:
Net income	$ 526,458	$ 137,038	$ 607,344	$ 152,117
Effect of Dilutive Securities:
Redemption of units to common shares	11,925	2,467	13,776	2,758
Diluted Earnings:
Income attributable to SL Green common stockholders	$ 538,383	$ 139,505	$ 621,120	$ 154,875
Basic Earnings:
Shares available to common stockholders (in shares)	83,578,000	78,046,000	81,632,000	77,936,000
Effect of Dilutive Securities
Redemption of units to common shares (in shares)	1,912,000	1,325,000	1,858,000	1,413,000
Exchangeable senior debentures					0	0		0	0		0	0
Stock-based compensation plans (in shares)	520,000	420,000	505,000	422,000
Interest rate (as a percent)					3.00%	3.00%	3.00%	3.00%	3.00%	3.00%	4.00%	4.00%	4.00%
Diluted Shares (in shares)	86,010,000	79,791,000	83,995,000	79,771,000
Common stock shares excluded from the diluted shares outstanding (in shares)	579,000	806,000	654,000	810,000