Accumulated Other Comprehensive Loss of the Company (Details) (USD $)	9 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			$ (29,587,000)
Ending balance	(19,249,000)		(29,587,000)
SL Green Realty Corporation
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(29,587,000)
Other comprehensive (loss) income before reclassifications	5,444,000
Amounts reclassified from accumulated other comprehensive income (loss)	4,894,000
Ending balance	(19,249,000)
SL Green Realty Corporation | Unrealized Gains (Losses) on Marketable Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(16,834,000)	[1]
Other comprehensive (loss) income before reclassifications	(121,000)	[1]
Amounts reclassified from accumulated other comprehensive income (loss)	1,222,000	[1]
Ending balance	(15,733,000)	[1]
SL Green Realty Corporation | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	3,310,000
Other comprehensive (loss) income before reclassifications	317,000
Amounts reclassified from accumulated other comprehensive income (loss)	0
Ending balance	3,627,000
Deferred net losses from terminated hedges	(14,300,000)		(15,000,000)
SL Green Realty Corporation | Joint venture | Unrealized Gains (Losses) on Marketable Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(16,063,000)	[2]
Other comprehensive (loss) income before reclassifications	5,248,000	[2]
Amounts reclassified from accumulated other comprehensive income (loss)	3,672,000	[2]
Ending balance	$ (7,143,000)	[2]

[1] Amount reclassified from accumulated other comprehensive income (loss) is included in interest expense in the respective consolidated statements of income. As of September 30, 2013 and December 31, 2012, the deferred net losses from these terminated hedges, which is included in accumulated other comprehensive loss relating to net unrealized gain on derivative instrument, was approximately $14.3 million and $15.0 million, respectively.

[2] Amount reclassified from accumulated other comprehensive income (loss) is included in equity in net income from unconsolidated joint ventures in the respective consolidated statements of income.