Property Acquisitions (Details) (USD $)	1 Months Ended										12 Months Ended				1 Months Ended
	Oct. 31, 2014		Sep. 30, 2014		Aug. 31, 2014		Jul. 31, 2014		May 31, 2014		Dec. 31, 2014		Dec. 31, 2013		Nov. 30, 2013		Apr. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012		Jan. 31, 2012
Recognized Identifiable Assets Acquired and Liabilities Assumed
Approximate Square Feet (sqft)											33,891,036
Fixed rate debt											$ 4,736,709,000		$ 4,130,629,000
Series J Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Fixed rate debt											4,000,000	[1]	0	[1]
102 Greene Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land	11,288,000	[2]
Building and building leasehold	20,962,000	[2]
Above market lease value	0	[2]
Acquired in-place leases	0	[2]
Other assets, net of other liabilities	0	[2]
Assets acquired	32,250,000	[2]
Mark-to-market assumed debt	0	[2]
Below market lease value	0	[2]
Derivatives	0	[2]
Liabilities assumed	0	[2]
Purchase price allocation	32,250,000	[2]
Net consideration funded by us at closing, excluding consideration financed by debt	32,250,000	[2]
Equity and/or debt investment held	0	[2]
Debt assumed	0	[2]
635 Madison Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land			153,745,000	[2],[3]
Building and building leasehold			0	[2],[3]
Above market lease value			0	[2],[3]
Acquired in-place leases			0	[2],[3]
Other assets, net of other liabilities			0	[2],[3]
Assets acquired			153,745,000	[2],[3]
Mark-to-market assumed debt			0	[2],[3]
Below market lease value			0	[2],[3]
Derivatives			0	[2],[3]
Liabilities assumed			0	[2],[3]
Purchase price allocation			153,745,000	[2],[3]
Net consideration funded by us at closing, excluding consideration financed by debt			153,745,000	[2],[3]
Equity and/or debt investment held			0	[2],[3]
Debt assumed			0	[2],[3]
635 Madison Avenue | Series J Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units			4,000,000
752 Madison Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land					282,415,000	[2],[4]
Building and building leasehold					0	[2],[4]
Above market lease value					0	[2],[4]
Acquired in-place leases					0	[2],[4]
Other assets, net of other liabilities					0	[2],[4]
Assets acquired					282,415,000	[2],[4]
Mark-to-market assumed debt					0	[2],[4]
Below market lease value					0	[2],[4]
Derivatives					0	[2],[4]
Liabilities assumed					0	[2],[4]
Purchase price allocation					282,415,000	[2],[4]
Net consideration funded by us at closing, excluding consideration financed by debt					282,415,000	[2],[4]
Equity and/or debt investment held					0	[2],[4]
Debt assumed					0	[2],[4]
Ownership interest in consolidated joint venture (as a percent)																										80.00%
719 Seventh Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land							14,402,000	[2],[5]
Building and building leasehold							26,747,000	[2],[5]
Above market lease value							0	[2],[5]
Acquired in-place leases							0	[2],[5]
Other assets, net of other liabilities							0	[2],[5]
Assets acquired							41,149,000	[2],[5]
Mark-to-market assumed debt							0	[2],[5]
Below market lease value							0	[2],[5]
Derivatives							0	[2],[5]
Liabilities assumed							0	[2],[5]
Purchase price allocation							41,149,000	[2],[5]
Net consideration funded by us at closing, excluding consideration financed by debt							41,149,000	[2],[5]
Equity and/or debt investment held							0	[2],[5]
Debt assumed							0	[2],[5]
Ownership interest in consolidated joint venture (as a percent)							75.00%
719 Seventh Avenue | Series L Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units							14,100,000
719 Seventh Avenue | Series K Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units							9,500,000
115 Spring Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land							15,938,000	[2]
Building and building leasehold							37,187,000	[2]
Above market lease value							0	[2]
Acquired in-place leases							0	[2]
Other assets, net of other liabilities							0	[2]
Assets acquired							53,125,000	[2]
Mark-to-market assumed debt							0	[2]
Below market lease value							0	[2]
Derivatives							0	[2]
Liabilities assumed							0	[2]
Purchase price allocation							53,125,000	[2]
Net consideration funded by us at closing, excluding consideration financed by debt							53,125,000	[2]
Equity and/or debt investment held							0	[2]
Debt assumed							0	[2]
388-390 Greenwich Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land									558,777,000	[2],[6]
Building and building leasehold									1,037,729,000	[2],[6]
Above market lease value									0	[2],[6]
Acquired in-place leases									0	[2],[6]
Other assets, net of other liabilities									6,495,000	[2],[6]
Assets acquired									1,603,001,000	[2],[6]
Mark-to-market assumed debt									0	[2],[6]
Below market lease value									0	[2],[6]
Derivatives									18,001,000	[2],[6]
Liabilities assumed									18,001,000	[2],[6]
Purchase price allocation									1,585,000,000	[2],[6]
Net consideration funded by us at closing, excluding consideration financed by debt									208,614,000	[2],[6]
Equity and/or debt investment held									148,025,000	[2],[6]
Debt assumed									1,162,379,000	[2],[6]
Economic interest									49.65%
Value of interest									1,585,000,000
Face amount of loan									1,450,000,000
Notional value									504,000,000
Purchase price fair value adjustment recognized									71,400,000
Business Acquisition, Pro Forma Information [Abstract]
Actual revenues since acquisition											1,519,978,000
Actual net income since acquisition											545,863,000
Pro forma revenues											1,562,206,000		1,481,021,000
Pro forma income from continuing operations											298,679,000	[7]	205,437,000	[7]
Pro forma basic earnings per share											$ 4.60		$ 2.10
Pro forma diluted earnings per share											$ 4.58		$ 2.09
Pro forma basic earnings per unit											4.60		2.10
Pro forma diluted earnings per unit											4.58		2.09
315 West 33rd Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land															195,834,000	[8]
Building and building leasehold															164,429,000	[8]
Above market lease value															7,084,000	[8]
Acquired in-place leases															26,125,000	[8]
Other assets, net of other liabilities															1,142,000	[8]
Assets acquired															394,614,000	[8]
Mark-to-market assumed debt															0	[8]
Below market lease value															7,839,000	[8]
Liabilities assumed															7,839,000	[8]
Purchase price allocation															386,775,000	[8]
Net consideration funded by us at closing, excluding consideration financed by debt															386,775,000	[8]
Equity and/or debt investment held															0	[8]
Debt assumed															0	[8]
Assemblage of Retail Development Properties on Fifth Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land															135,513,000	[8]
Building and building leasehold															10,487,000	[8]
Above market lease value															0	[8]
Acquired in-place leases															0	[8]
Other assets, net of other liabilities															0	[8]
Assets acquired															146,000,000	[8]
Mark-to-market assumed debt															0	[8]
Below market lease value															0	[8]
Liabilities assumed															0	[8]
Purchase price allocation															146,000,000	[8]
Net consideration funded by us at closing, excluding consideration financed by debt															146,000,000	[8]
Equity and/or debt investment held															0	[8]
Debt assumed															0	[8]
16 Court Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land																	19,217,000	[9]
Building and building leasehold																	63,210,000	[9]
Above market lease value																	5,122,000	[9]
Acquired in-place leases																	9,422,000	[9]
Other assets, net of other liabilities																	3,380,000	[9]
Assets acquired																	100,351,000	[9]
Mark-to-market assumed debt																	294,000	[9]
Below market lease value																	3,885,000	[9]
Liabilities assumed																	4,179,000	[9]
Purchase price allocation																	96,172,000	[9]
Net consideration funded by us at closing, excluding consideration financed by debt																	4,000,000	[9]
Equity and/or debt investment held																	13,835,000	[9]
Debt assumed																	84,642,000	[9]
Mortgage encumbering the property																	84,600,000
Purchase price fair value adjustment																	(2,300,000)
248-252 Bedford Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land																			10,865,000	[10]
Building and building leasehold																			44,035,000	[10]
Above market lease value																			0	[10]
Acquired in-place leases																			0	[10]
Other assets, net of other liabilities																			0	[10]
Assets acquired																			54,900,000	[10]
Mark-to-market assumed debt																			0	[10]
Below market lease value																			0	[10]
Liabilities assumed																			0	[10]
Purchase price allocation																			54,900,000	[10]
Net consideration funded by us at closing, excluding consideration financed by debt																			21,782,000	[10]
Equity and/or debt investment held																			0	[10]
Debt assumed																			0	[10]
Face amount of loan																			22,000,000.0
Stated interest rate of preferred partnership units issued (as a percent)																			90.00%
131-137 Spring Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land																					27,021,000
Building and building leasehold																					105,342,000
Above market lease value																					179,000
Acquired in-place leases																					7,046,000
Other assets, net of other liabilities																					0
Assets acquired																					139,588,000
Fair value adjustment to mortgage note payable																					0
Below market lease value																					17,288,000
Liabilities assumed																					17,288,000
Purchase price allocation																					122,300,000
Net consideration funded by us at closing, excluding consideration financed by debt																					122,300,000
Equity and/or debt investment held																					0
Debt assumed																					0
985-987 Third Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land																					5,400,000	[11]
Building and building leasehold																					12,600,000	[11]
Above market lease value																					0	[11]
Acquired in-place leases																					0	[11]
Other assets, net of other liabilities																					0	[11]
Assets acquired																					18,000,000	[11]
Fair value adjustment to mortgage note payable																					0	[11]
Below market lease value																					0	[11]
Liabilities assumed																					0	[11]
Purchase price allocation																					18,000,000	[11]
Net consideration funded by us at closing, excluding consideration financed by debt																					18,000,000	[11]
Equity and/or debt investment held																					0	[11]
Debt assumed																					0	[11]
Approximate Square Feet (sqft)							13,678	[12]
635-641 Sixth Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land																							69,848,000
Building and building leasehold																							104,474,000
Above market lease value																							0
Acquired in-place leases																							7,727,000
Other assets, net of other liabilities																							0
Assets acquired																							182,049,000
Fair value adjustment to mortgage note payable																							0
Below market lease value																							9,049,000
Liabilities assumed																							9,049,000
Purchase price allocation																							173,000,000
Net consideration funded by us at closing, excluding consideration financed by debt																							173,000,000
Equity and/or debt investment held																							0
Debt assumed																							0	0	[13]
304 Park Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land																								54,189,000	[13]
Building and building leasehold																								75,619,000	[13]
Above market lease value																								2,824,000	[13]
Acquired in-place leases																								8,265,000	[13]
Other assets, net of other liabilities																								0	[13]
Assets acquired																								140,897,000	[13]
Fair value adjustment to mortgage note payable																								0	[13]
Below market lease value																								5,897,000	[13]
Liabilities assumed																								5,897,000	[13]
Purchase price allocation																								135,000,000	[13]
Net consideration funded by us at closing, excluding consideration financed by debt																								135,000,000	[13]
Equity and/or debt investment held																								0	[13]
Consideration in cash																								102,000,000
Value of preferred operating partnership units issued																								33,000,000
Stonehenge Properties
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land																										65,533,000	[14]
Building and building leasehold																										128,457,000	[14]
Above market lease value																										594,000	[14]
Acquired in-place leases																										9,573,000	[14]
Other assets, net of other liabilities																										2,190,000	[14]
Assets acquired																										206,347,000	[14]
Fair value adjustment to mortgage note payable																										0	[14]
Below market lease value																										13,239,000	[14]
Liabilities assumed																										13,239,000	[14]
Net consideration funded by us at closing, excluding consideration financed by debt																										78,121,000	[14]
Equity and/or debt investment held																										0	[14]
Debt assumed																										0	[14]
Ownership interest in consolidated joint venture (as a percent)																										80.00%
Manhattan
Recognized Identifiable Assets Acquired and Liabilities Assumed
Price of acquisition																										193,108,000	[14]
Manhattan | Series G Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Mortgage encumbering the property																										47,600,000
Retail properties
Recognized Identifiable Assets Acquired and Liabilities Assumed
Fixed rate debt																										8,500,000.0
Multifamily properties
Recognized Identifiable Assets Acquired and Liabilities Assumed
Number of units (unit)																										385
Approximate Square Feet (sqft)																										488,000
Fixed rate debt																										$ 100,000,000.0
Interest rate, fixed rate debt (as a percent)																										4.10%
Apartments | 248-252 Bedford Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Number of units (unit)																			72
Townhouses | 248-252 Bedford Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Number of units (unit)																			12

[1] In connection with the acquisition of a commercial real estate property, the Operating Partnership issued $4.0 million or 4,000 3.75% Series J Preferred Units of limited partnership interest, or the Series J Preferred Units, with a mandatory liquidation preference of $1,000.00 per unit. The Series J Preferred Units can be redeemed in cash by the Operating Partnership on the earlier of (i) the date of the sale of the property or (ii) April 30, 2051 or at the option of the unitholders as further prescribed in the related agreement.

[2] We are currently in the process of analyzing the purchase price allocation and, as such, we have not allocated any value to intangible assets such as above- and below-market lease or in-place leases.

[3] This property was acquired inclusive of the issuance of $4.0 million aggregate liquidation preference of Series J Preferred Units of limited partnership interest of the Operating Partnership.

[4] In January 2012, a separate joint venture in which an SL Green entity holds an 80% interest acquired the ground tenancy position.

[5] We, along with our joint venture partner, acquired this property inclusive of the issuance of $14.1 million aggregate liquidation preference of Series L Preferred Units of limited partnership interest of the Operating Partnership and $9.5 million aggregate liquidation preference of Series K Preferred Units of limited partnership interest of the Operating Partnership. We hold a 75.0% controlling interest in this joint venture.

[6] In May 2014, we acquired Ivanhoe Cambridge, Inc.'s 49.65% economic interest in this property, thereby consolidating full ownership of the property. The transaction valued the consolidated interests at $1.585 billion. Simultaneous with the closing, we refinanced the previous mortgage with a $1.45 billion mortgage. We also assumed the existing derivative instruments, which swapped $504.0 million of the mortgage to fixed rate. We recognized a purchase price fair value adjustment of $71.4 million upon closing of this transaction. This property, which we initially acquired in December 2007, was previously accounted for as an investment in unconsolidated joint ventures.

[7] The pro forma income from continuing operations for the years ended December 31, 2014 and 2013 includes the effect of the new financing necessary to complete the acquisition and the preliminary allocation of purchase price in connection with the changes in depreciation and amortization. In addition, the pro forma income from continuing operations for the year ended December 31, 2013 was adjusted to include the purchase price fair value adjustment, as though the acquisition was completed on January 1, 2013. The pro forma income from continuing operations for the year ended December 31, 2014 excludes this purchase price fair value adjustment.

[8] During the year ended December 31, 2014, we finalized the purchase price allocation based on a third party appraisal and additional facts and circumstances that existed at the acquisition dates. These adjustments did not have a material impact to our consolidated statement of income for the year ended December 31, 2014.

[9] In April 2013, we acquired interests from our joint venture partner, City Investment Fund, or CIF, in 16 Court Street in Brooklyn for $4.0 million. We have consolidated the ownership of the building. The transaction valued the consolidated interest at $96.2 million, inclusive of the $84.6 million mortgage encumbering the property. In April 2014, we repaid the mortgage. We recognized a purchase price fair value adjustment of $(2.3) million upon the closing of this transaction. This property, which we initially acquired in July 2007, was previously accounted for as an investment in unconsolidated joint ventures.

[10] In March 2013, we, along with Magnum Real Estate Group, acquired 84 residential units, consisting of 72 apartment units and 12 townhouses, located at 248-252 Bedford Avenue, Williamsburg, Brooklyn for $54.9 million. Simultaneous with the closing on this property, the joint venture closed on a $22.0 million mortgage loan which was later refinanced in June 2014. The property is above a commercial property already owned by us. We hold a 90.0% controlling interest in this joint venture.

[11] This property was subsequently sold in July 2014. See Note 4, "Properties Held for Sale and Dispositions."

[12] The gain on sale for 2 Herald Square, 985-987 Third Avenue, 673 First Avenue, 333 West 34th Street, and 292 Madison Avenue are net of a $2.5 million, $1.3 million, $3.4 million, $3.0 million and $1.5 million employee compensation award, respectively, accrued in connection with the realization of this investment gain as a bonus to certain employees that were instrumental in realizing the gain on sale.

[13] This property was acquired with $102.0 million in cash and $33.0 million in units of limited partnership interest of the Operating Partnership.

[14] In January 2012, we acquired five retail and two multifamily properties in Manhattan for $193.1 million. This property was acquired inclusive of the issuance of $47.6 million aggregate liquidation preference of Series G Preferred Units of limited partnership interest of the Operating Partnership. Simultaneous with the closing, we financed the multifamily component, which encompasses 385 units and approximately 488,000 square feet (unaudited), with an aggregate $100.0 million fixed rate mortgage which bears interest at 4.1% and one of the retail properties financed with an $8.5 million fixed rate mortgage. We hold an 80.0% interest in this joint venture which we consolidate as it is a VIE and we have been designated as the primary beneficiary. In February 2013, we sold one of the retail properties, which is further described in Note 4, "Properties Held for Sale and Dispositions."