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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stockholders' Equity
Net income attributable to SL Green common stockholders	$ 56,787	$ 64,688	$ 235,539	$ 146,090	$ 37,120	$ 37,025	$ 8,276	$ 18,909	$ 503,104	$ 101,330	$ 155,984
Basic weighted average common shares outstanding (in shares)									95,774,000	92,269,000	89,319,000
Common stock shares excluded from the diluted shares outstanding									737,361	964,789	627,000
SL Green Operating Partnership
Stockholders' Equity
Net income attributable to SL Green common stockholders									$ 521,571	$ 104,353	$ 161,581
Basic weighted average common shares outstanding (in shares)									99,288,000	95,004,000	92,526,000
Stock-based compensation plans (shares)									408,000	262,000	347,000
Diluted weighted average common units outstanding (shares)									99,696,000	95,266,000	92,873,000
Common stock shares excluded from the diluted shares outstanding									737,361	964,789	627,000