Accumulated Other Comprehensive Loss of the Company (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Ending Balance	$ (6,980,000)		$ (15,211,000)
Deferred net losses from terminated hedges	11,800,000		13,800,000		15,000,000
SL Green Realty Corp
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	(15,211,000)		(29,587,000)		(28,445,000)
Other comprehensive loss before reclassifications	(421,000)		7,573,000		(15,101,000)
Amounts reclassified from accumulated other comprehensive income	8,652,000		6,803,000		13,959,000
Ending Balance	(6,980,000)		(15,211,000)		(29,587,000)
SL Green Realty Corp | Net unrealized loss on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	(15,125,000)	[1]	(16,834,000)	[1]	(17,510,000)	[1]
Other comprehensive loss before reclassifications	(576,000)	[1]	(168,000)	[1]	(1,124,000)	[1]
Amounts reclassified from accumulated other comprehensive income	6,203,000	[1]	1,877,000	[1]	1,800,000	[1]
Ending Balance	(9,498,000)	[1]	(15,125,000)	[1]	(16,834,000)	[1]
SL Green Realty Corp | Unrealized gain and (loss) on marketable securities
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	4,784,000		3,310,000		6,466,000
Other comprehensive loss before reclassifications	(2,692,000)		1,474,000		(4,879,000)
Amounts reclassified from accumulated other comprehensive income	521,000		0		1,723,000
Ending Balance	2,613,000		4,784,000		3,310,000
SL Green Realty Corp | Joint venture | Net unrealized loss on derivative instruments
Accumulated Other Comprehensive Income (Loss) of the Company [Roll Forward]
Beginning Balance	(4,870,000)	[2]	(16,063,000)	[2]	(17,401,000)	[2]
Other comprehensive loss before reclassifications	2,847,000	[2]	6,267,000	[2]	(9,098,000)	[2]
Amounts reclassified from accumulated other comprehensive income	1,928,000	[2]	4,926,000	[2]	10,436,000	[2]
Ending Balance	$ (95,000)	[2]	$ (4,870,000)	[2]	$ (16,063,000)	[2]

[1] Amount reclassified from accumulated other comprehensive income (loss) is included in interest expense in the respective consolidated statements of income. As of December 31, 2014, 2013 and 2012, the deferred net losses from these terminated hedges, which is included in accumulated other comprehensive loss relating to net unrealized loss on derivative instrument, was $11.8 million , $13.8 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.