Segment Information (Schedule of Reconciliation of Income from Continuing Operations to Net Income Attributable to SL Green Common Stockholders)(Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reconciliation of income from continuing operations to net income attributable to SL Green common stockholders
Net income before equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, net, depreciable real estate reserves, and gain on sale of investment in marketable securities	$ 35,813	$ (70,463)	$ 87,133	$ (61,648)
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	13,089	33,448	15,136	43,363
(Loss) gain on sale of real estate, net	(3,823)	196,580	(3,256)	210,353
Depreciable real estate reserves	(29,064)	(10,387)	(85,336)	(10,387)
(Loss) gain on sale of investment in marketable securities	0	(83)	3,262	(83)
Net income	$ 16,015	$ 149,095	$ 16,939	$ 181,598

Depreciable Real Estate Reserves, Effect on Earnings

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- Definition

This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before realized gains (losses) on disposals of equity method investments, extraordinary items, and noncontrolling interest.

+ References

No definition available.

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- Definition

Amount of gain (loss) on sale or disposal of an equity method investment.

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No definition available.

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- Definition

The net gain (loss) resulting from sales and other disposals of real estate owned for investment purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.14(d))
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- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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-Subparagraph (a),(c)-(e)
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- References

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- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 4K
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