Accumulated Other Comprehensive Loss of the Operating Partnership (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 Operating Partnership
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(30,649,000)
Other comprehensive (loss) income before reclassifications	5,789,000
Amounts reclassified from accumulated other comprehensive income (loss)	5,039,000
Ending balance	(19,821,000)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	3,429,000
Other comprehensive (loss) income before reclassifications	306,000
Amounts reclassified from accumulated other comprehensive income (loss)	0
Ending balance	3,735,000
Deferred net losses from terminated hedges	(14,800,000)		(15,500,000)
Unrealized Gains (Losses) on Marketable Securities [Member] | SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(17,438,000)	[1]
Other comprehensive (loss) income before reclassifications	(20,000)	[1]
Amounts reclassified from accumulated other comprehensive income (loss)	1,258,000	[1]
Ending balance	(16,200,000)	[1]
Joint venture | Unrealized Gains (Losses) on Marketable Securities [Member] | SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(16,640,000)	[2]
Other comprehensive (loss) income before reclassifications	5,503,000	[2]
Amounts reclassified from accumulated other comprehensive income (loss)	3,781,000	[2]
Ending balance	$ (7,356,000)	[2]

[1] Amount reclassified from accumulated other comprehensive income (loss) is included in interest expense in the respective consolidated statements of income.

[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.