Noncontrolling Interest-Rollforward (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 SL Green Operating Partnership [Member]	Dec. 31, 2012 SL Green Operating Partnership [Member]	Dec. 31, 2011 SL Green Operating Partnership [Member]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Distributions to noncontrolling interests			$ (11,809)			$ (2,695)	$ (3,296)
Issuance of common units						14,270	42,239
Redemption of common units						(17,287)	(87,513)
Net income	1,110	567	1,909	4,876		1,909	5,597
Accumulated other comprehensive income (loss)	(25)	(59)	490	(396)		490	(388)
Fair value adjustment						38,452	61,238
Balance at the end of period	$ 248,046		$ 248,046		$ 212,907	$ 248,046	$ 212,907	$ 195,030