Partners' Capital of the Operating Partnership - EPS (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Stockholders' Equity
Income attributable to SL Green common stockholders	$ 43,277	$ 146,090
Basic weighted average common shares outstanding (shares)	98,402,000	95,117,000
Common stock shares excluded from the diluted shares outstanding (shares)	203,975	860,720
SL Green Operating Partnership
Stockholders' Equity
Income attributable to SL Green common stockholders	$ 45,020	$ 150,819
Basic weighted average common shares outstanding (shares)	102,366,000	98,196,000
Stock-based compensation plans (shares)	653,000	520,000
Diluted weighted average common units outstanding (shares)	103,019,000	98,716,000
Common stock shares excluded from the diluted shares outstanding (shares)	203,975	860,720