Equity (Details 5) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic Earnings:
Net income attributable to SL Green common stockholders	$ 19,956	$ 7,732	$ 103,040	$ 25,256	$ 2,808	$ 7,079	$ 526,458	$ 80,887	$ 155,984	$ 617,232	$ 270,826
Effect of Dilutive Securities:
Redemption of units to common shares									5,597	14,629	4,574
Diluted Earnings:
Income attributable to SL Green common stockholders									$ 161,581	$ 631,861	$ 275,400
Basic Shares:
Basic weighted average common shares outstanding (in shares)									89,319,000	83,762,000	78,101,000
Effect of Dilutive Securities
Redemption of units to common shares									3,207,000	1,985,000	1,321,000
Stock-based compensation plans (in shares)									347,000	497,000	339,000
Diluted Shares									92,873,000	86,244,000	79,761,000
Common stock shares excluded from the diluted shares outstanding									627,000	680,000	804,800
3.0% exchangeable senior debentures due 2017
Effect of Dilutive Securities
Interest rate (as a percent)	3.00%								3.00%
3.0% exchangeable senior debentures due 2027
Effect of Dilutive Securities
Interest rate (as a percent)	3.00%								3.00%
4.0% exchangeable senior debentures due 2025
Effect of Dilutive Securities
Interest rate (as a percent)	4.00%								4.00%