Accumulated Other Comprehensive Loss of the Operating Partnership (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance		$ (6,980,000)
Ending Balance	(11,810,000)	(6,980,000)
Deferred net losses from terminated hedges	11,300,000	11,800,000
SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	(7,256,000)
Other comprehensive (loss) income before reclassifications	(8,108,000)
Amounts reclassified from accumulated other comprehensive income	3,078,000
Ending Balance	(12,286,000)
Deferred net losses from terminated hedges	11,700,000	12,200,000
Net unrealized loss on derivative instruments \| SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	(9,845,000)
Other comprehensive (loss) income before reclassifications	(7,521,000)
Amounts reclassified from accumulated other comprehensive income	2,747,000
Ending Balance	(14,619,000)
Unrealized gain and (loss) on marketable securities \| SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	2,689,000
Other comprehensive (loss) income before reclassifications	650,000
Amounts reclassified from accumulated other comprehensive income	0
Ending Balance	3,339,000
Joint venture \| Net unrealized loss on derivative instruments \| SL Green Operating Partnership
Accumulated Other Comprehensive Income (Loss) of the Operating Partnership [Roll Forward]
Beginning Balance	(100,000)
Other comprehensive (loss) income before reclassifications	(1,237,000)
Amounts reclassified from accumulated other comprehensive income	331,000
Ending Balance	$ (1,006,000)

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Other Comprehensive Income (Loss), Deferred Net Loss from Terminated Hedges

+ References

No definition available.

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- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14A

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e681-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 31

-Article 5

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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