Corporate Indebtedness (Details) (USD $)	3 Months Ended				3 Months Ended		1 Months Ended	3 Months Ended					3 Months Ended		3 Months Ended			1 Months Ended			3 Months Ended									3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Share of Joint Venture Debt	Mar. 31, 2014 2012 Credit Facility	Nov. 30, 2012 2012 Credit Facility	Nov. 30, 2012 Revolving credit facility extension	Mar. 31, 2014 Revolving credit facility	Mar. 31, 2014 Revolving credit facility Maximum	Mar. 31, 2014 Revolving credit facility Minimum	Mar. 31, 2014 Term loan	Mar. 31, 2014 Term Loan and Senior Unsecured Notes	Mar. 31, 2014 3.00% Senior unsecured notes maturing on October 15, 2017	Oct. 31, 2010 3.00% Senior unsecured notes maturing on October 15, 2017	Mar. 31, 2013 4.0% exchangeable senior debentures due 2025	Mar. 31, 2014 4.0% exchangeable senior debentures due 2025	Mar. 31, 2007 3.0% exchangeable senior debentures due 2027	Jun. 30, 2005 Trust Preferred Securities	Mar. 31, 2014 Trust Preferred Securities	Mar. 31, 2014 Mortgages and other loans payable	Mar. 31, 2014 LIBOR Revolving credit facility	Mar. 31, 2014 LIBOR Revolving credit facility Maximum	Mar. 31, 2014 LIBOR Revolving credit facility Minimum	Mar. 31, 2014 LIBOR Term loan	Mar. 31, 2014 LIBOR Term loan Maximum	Mar. 31, 2014 LIBOR Term loan Minimum	Mar. 31, 2014 LIBOR Trust Preferred Securities	Mar. 31, 2014 Senior Unsecured Notes	Dec. 31, 2013 Senior Unsecured Notes	Mar. 31, 2014 Senior Unsecured Notes 5.88% Senior unsecured notes maturing on August 15, 2014		Dec. 31, 2013 Senior Unsecured Notes 5.88% Senior unsecured notes maturing on August 15, 2014		Mar. 31, 2014 Senior Unsecured Notes 6.00% Senior unsecured notes maturing on March 31, 2016		Dec. 31, 2013 Senior Unsecured Notes 6.00% Senior unsecured notes maturing on March 31, 2016		Mar. 31, 2014 Senior Unsecured Notes 3.00% Senior unsecured notes maturing on October 15, 2017		Dec. 31, 2013 Senior Unsecured Notes 3.00% Senior unsecured notes maturing on October 15, 2017		Mar. 31, 2014 Senior Unsecured Notes 5.00% senior unsecured notes maturing on August 15, 2018		Dec. 31, 2013 Senior Unsecured Notes 5.00% senior unsecured notes maturing on August 15, 2018		Mar. 31, 2014 Senior Unsecured Notes 7.75% Senior unsecured notes maturing on March 15, 2020		Dec. 31, 2013 Senior Unsecured Notes 7.75% Senior unsecured notes maturing on March 15, 2020		Mar. 31, 2014 Senior Unsecured Notes 4.50% senior unsecured notes maturing on December 1, 2022		Dec. 31, 2013 Senior Unsecured Notes 4.50% senior unsecured notes maturing on December 1, 2022		Mar. 31, 2014 Senior Unsecured Notes 4.0% exchangeable senior debentures due 2025		Dec. 31, 2013 Senior Unsecured Notes 4.0% exchangeable senior debentures due 2025		Mar. 31, 2014 Senior Unsecured Notes 3.0% exchangeable senior debentures due 2027		Dec. 31, 2013 Senior Unsecured Notes 3.0% exchangeable senior debentures due 2027
Corporate Indebtedness
Face amount of loan						$ 1,600,000,000
Increase in maximum borrowing capacity											383,000,000
Decrease in basis spread on variable rate (percent)								0.25%
Extension fee (percent)								0.10%
Maximum borrowing capacity	300,000,000						1,200,000,000.0				783,000,000.0
Number of extension options (extensions)							2
Extension option available							6 months
Maximum borrowing capacity, optional expansion							1,500,000,000.0
Interest rate added to base rate (as a percent)																					1.45%	1.75%	1.00%	1.40%	1.90%	0.95%	1.25%
Fee on the unused balance, payable quarterly in arrears (as a percent)									0.35%	0.15%
Facility fee on total commitments, payable quarterly in arrears (as a percent)										0.30%
Letters of credit					71,600,000
Outstanding under line of credit facility	0		220,000,000								783,000,000
Ability to borrow under line of credit facility					1,100,000,000
Debt origination and legal costs					2,800,000
Debt disclosures by scheduled maturity date
Unpaid Principal Balance																												1,386,221,000		75,898,000	[1],[2]			255,308,000	[1],[2]			345,000,000	[3]			250,000,000	[4]			250,000,000	[4]			200,000,000	[4]			7,000	[2],[5]			10,008,000
Accreted Balance	2,124,397,000		1,739,330,000																									1,341,397,000	1,339,330,000	75,898,000	[1],[2]	75,898,000	[1],[2]	255,217,000	[1],[2]	255,206,000	[1],[2]	300,571,000	[3]	297,837,000	[3]	249,696,000	[4]	249,681,000	[4]	250,000,000	[4]	250,000,000	[4]	200,000,000	[4]	200,000,000	[4]	7,000	[2],[5]	7,000	[2],[5]	10,008,000		10,701,000
Coupon Rate (as a percent)																			5.61%											5.88%	[1],[2],[6]			6.00%	[1],[2],[6]			3.00%	[3],[6]			5.00%	[4],[6]			7.75%	[4],[6]			4.50%	[4],[6]			4.00%	[2],[5],[6]			3.00%	[6]
Effective Rate (as a percent)								1.62%			1.84%																			5.88%	[1],[2]			6.00%	[1],[2]			3.00%	[3]			5.00%	[4]			7.75%	[4]			4.50%	[4]			4.00%	[2],[5]			3.00%
Term																														10 years	[1],[2]			10 years	[1],[2]			7 years	[3]			7 years	[4]			10 years	[4]			10 years	[4]			20 years	[2],[5]			20 years
Debt instrument issued, value																		100,000,000.0
Premium on sale price to calculate exchange price of notes (as a percent)														30.00%			25.00%
Exchange price (in dollars per share)														$ 85.81		$ 1.3491	$ 173.30
Adjusted exchange rate for the debentures (in shares)													11.7153		7.7461
Amount of convertible debt recorded in equity														78,300,000
Debt Instrument, Unamortized Discount													44,400,000
Number of years for which securities will bear fixed rate of interest																		10 years
Scheduled Amortization
2014																				33,737,000
2015																				47,356,000
2016																				55,980,000
2017																				61,213,000
2018																				64,205,000
Thereafter																				246,825,000
Total amortization of debt																				509,316,000
Principal Repayments
2014				41,973,000																358,489,000
2015				45,362,000																229,537,000
2016				559,777,000																593,400,000
2017				932,912,000																1,086,579,000
2018				28,000																21,363,000
Thereafter				353,585,000																2,172,338,000
Total principal repayments				1,933,637,000																4,461,706,000
Scheduled Amortization and Principal Repayments
2014	468,124,000											75,898,000
2015	276,900,000											7,000
2016	904,688,000											255,308,000
2017	1,502,800,000											355,008,000
2018	335,568,000											250,000,000
Thereafter	3,752,163,000											1,233,000,000							100,000,000
Total amortization of debt and principal repayments	7,240,243,000											2,169,221,000							100,000,000
Interest expense
Interest expense	80,712,000	81,216,000
Interest income	(532,000)	(441,000)
Interest expense, net	80,180,000	80,775,000
Interest capitalized	$ 4,141,000	$ 3,062,000

[1] 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 11.7153 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 guaranteed by ROP. On the issuance date, $78.3 million of the debt balance was recorded in equity. As of March 31, 2014, $44.4 million remained to be amortized into the debt balance.

[2] Issued by ROP.

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

[4] 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.

[5] 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 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.

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