Corporate Indebtedness (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Oct. 06, 2010	Mar. 20, 2007
Debt disclosures by scheduled maturity date
Accreted Balance	$ 2,107,078,000		$ 1,739,330,000
Senior unsecured notes
Debt disclosures by scheduled maturity date
Unpaid Principal Balance	1,310,323,000
Accreted Balance	1,274,078,000		1,339,330,000
Senior unsecured notes | 6.00% Senior unsecured notes maturing on March 31, 2016
Debt disclosures by scheduled maturity date
Unpaid Principal Balance	255,308,000	[1]
Accreted Balance	255,250,000	[1]	255,206,000	[1]
Coupon Rate (as a percent)	6.00%	[1],[2]
Effective rate (as a percent)	6.00%	[1]
Term	10 years	[1]
Senior unsecured notes | 3.00% Senior unsecured notes maturing on October 15, 2017
Debt disclosures by scheduled maturity date
Unpaid Principal Balance	345,000,000	[3]
Accreted Balance	309,069,000	[3]	297,837,000	[3]
Coupon Rate (as a percent)	3.00%	[2],[3]
Effective rate (as a percent)	3.00%	[3]
Term	7 years	[3]
Premium on sale price to calculate exchange price of notes (as a percent)					30.00%
Exchange price (in dollars per share)					$ 85.81
Adjusted exchange rate for the debentures (in shares)	12.1163
Amount of convertible debt recorded in equity					78,300,000
Debt Instrument, Unamortized Discount	35,900,000
Senior unsecured notes | 5.00% Senior unsecured notes maturing on August 15, 2018
Debt disclosures by scheduled maturity date
Unpaid Principal Balance	250,000,000	[4]
Accreted Balance	249,744,000	[4]	249,681,000	[4]
Coupon Rate (as a percent)	5.00%	[2],[4]
Effective rate (as a percent)	5.00%	[4]
Term	7 years	[4]
Senior unsecured notes | 7.75% Senior unsecured notes maturing on March 15, 2020
Debt disclosures by scheduled maturity date
Unpaid Principal Balance	250,000,000	[4]
Accreted Balance	250,000,000	[4]	250,000,000	[4]
Coupon Rate (as a percent)	7.75%	[2],[4]
Effective rate (as a percent)	7.75%	[4]
Term	10 years	[4]
Senior unsecured notes | 4.50% Senior unsecured notes maturing on December 1, 2022
Debt disclosures by scheduled maturity date
Unpaid Principal Balance	200,000,000	[4]
Accreted Balance	200,000,000	[4]	200,000,000	[4]
Coupon Rate (as a percent)	4.50%	[2],[4]
Effective rate (as a percent)	4.50%	[4]
Term	10 years	[4]
Senior unsecured notes | 4.00% Senior unsecured notes maturing on June 15, 2025
Debt disclosures by scheduled maturity date
Unpaid Principal Balance	7,000	[1],[5]
Accreted Balance	7,000	[1],[5]	7,000	[1],[5]
Coupon Rate (as a percent)	4.00%	[1],[2],[5]
Effective rate (as a percent)	4.00%	[1],[5]
Term	20 years	[1],[5]
Exchange price (in dollars per share)	$ 1.3491
Adjusted exchange rate for the debentures (in shares)	7.7461
Senior unsecured notes | 3.00% Senior unsecured notes maturing on March 30, 2027
Debt disclosures by scheduled maturity date
Unpaid Principal Balance	10,008,000	[6]
Accreted Balance	10,008,000	[6]	10,701,000	[6]
Coupon Rate (as a percent)	3.00%	[2],[6]
Effective rate (as a percent)	3.00%	[6]
Term	20 years	[6]
Premium on sale price to calculate exchange price of notes (as a percent)						25.00%
Exchange price (in dollars per share)						$ 173.30
Adjusted exchange rate for the debentures (in shares)	5.7952
Senior unsecured notes | Senior unsecured notes due August 15, 2014
Debt disclosures by scheduled maturity date
Unpaid Principal Balance	0	[1],[7]
Accreted Balance	$ 0	[1],[7]	$ 75,898,000	[1],[7]
Coupon Rate (as a percent)		[1],[2],[7]
Effective rate (as a percent)		[1],[7]
Term		[1],[7]

[1] Issued by ROP.

[2] Interest on the senior unsecured notes is payable semi-annually with principal and unpaid interest due on the scheduled maturity dates.

[3] Issued by the Operating Partnership. Interest on these exchangeable notes is payable semi-annually on April 15 and October 15. The notes had an initial exchange rate representing an exchange price that was set at a 30.0% premium to the last reported sale price of SL Green's common stock on October 6, 2010, or $85.81. The initial exchange rate is subject to adjustment under certain circumstances. The current exchange rate is 12.1163 shares of SL Green's common stock per $1,000 principal amount of these notes. The notes are senior unsecured obligations of the Operating Partnership and are exchangeable upon the occurrence of specified events and during the period beginning on the twenty-second scheduled trading day prior to the maturity date and ending on the second business day prior to the maturity date, into cash or a combination of cash and shares of SL Green's common stock, if any, at our option. As a result of meeting specified events (as defined in the Indenture Agreement), these notes are exchangeable commencing January 1, 2015 and will remain exchangeable through March 31, 2015. The notes are guaranteed by ROP. On the issuance date, $78.3 million of the debt balance was recorded in equity. As of December 31, 2014, $35.9 million remained to be amortized into the debt balance.

[4] Issued by the Company, the Operating Partnership and ROP, as co-obligors.

[5] Exchangeable senior debentures which are currently callable at par. In addition, the debentures can be put to ROP, at the option of the holder at par plus accrued and unpaid interest, on June 15, 2015 and 2020 and upon the occurrence of certain change of control transactions. As a result of the acquisition of all outstanding shares of common stock of Reckson, or the Reckson Merger, the adjusted exchange rate for the debentures is 7.7461 shares of SL Green's common stock per $1,000 of principal amount of debentures and the adjusted reference dividend for the debentures is $1.3491.

[6] Issued by the Operating Partnership. Interest on these remaining exchangeable notes is payable semi-annually on March 30 and September 30. The notes have an initial exchange rate representing an exchange price that was set at a 25.0% premium to the last reported sale price of the Company's common stock on March 20, 2007, or $173.30. The initial exchange rate is subject to adjustment under certain circumstances. The current exchange rate is 5.7952 shares of SL Green's common stock per $1,000 principal amount of these notes. The notes are senior unsecured obligations of the Operating Partnership and are exchangeable upon the occurrence of specified events and during the period beginning on the twenty-second scheduled trading day prior to the maturity date and ending on the second business day prior to the maturity date, into cash or a combination of cash and shares of SL Green's common stock, if any, at our option. The notes are currently redeemable at the Operating Partnership’s option. The Operating Partnership may be required to repurchase the notes on March 30, 2017 and 2022, and upon the occurrence of certain designated events.

[7] In August 2014, these notes were repaid at maturity.