Partners' Capital of the Operating Partnership-EPS (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Stockholders' Equity
Net income attributable to SL Green common stockholders	$ 37,120	$ 37,025	$ 8,276	$ 18,909	$ 19,956	$ 7,732	$ 103,040	$ 25,256	$ 101,330	$ 155,984	$ 617,232
Redemption of units to common shares									0	0	0
Income attributable to SLGOP common unitholders									104,353	161,581	631,861
Basic weighted average common shares outstanding (in shares)									92,269,000	89,319,000	83,762,000
Stock-based compensation plans (in shares)									262,000	347,000	497,000
Common stock shares excluded from the diluted shares outstanding									964,789	627,000	680,000
SL Green Operating Partnership
Stockholders' Equity
Net income attributable to SL Green common stockholders									104,353	161,581	631,861
Income attributable to SLGOP common unitholders									$ 104,353	$ 161,581	$ 631,861
Basic weighted average common shares outstanding (in shares)									95,004,000	92,526,000	85,747,000
Stock-based compensation plans (shares)									262,000	347,000	497,000
Diluted weighted average common units outstanding (shares)									95,266,000	92,873,000	86,244,000
Common stock shares excluded from the diluted shares outstanding									964,789	627,000	680,000
3.0% exchangeable senior debentures due 2017 | SL Green Operating Partnership
Stockholders' Equity
Interest rate (as a percent)	3.00%								3.00%
Stock-based compensation plans (in shares)									0	0	0
3.0% exchangeable senior debentures due 2027
Stockholders' Equity
Interest rate (as a percent)	3.00%								3.00%
Stock-based compensation plans (in shares)									0	0	0
3.0% exchangeable senior debentures due 2027 | SL Green Operating Partnership
Stockholders' Equity
Interest rate (as a percent)	3.00%								3.00%
Stock-based compensation plans (in shares)									0	0	0
4.0% exchangeable senior debentures due 2025
Stockholders' Equity
Interest rate (as a percent)	4.00%								4.00%
Stock-based compensation plans (in shares)									0	0	0
4.0% exchangeable senior debentures due 2025 | SL Green Operating Partnership
Stockholders' Equity
Interest rate (as a percent)	4.00%								4.00%
Stock-based compensation plans (in shares)									0	0	0