Investment in Unconsolidated Joint Ventures (Details 3) (USD $)	3 Months Ended										12 Months Ended					1 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	May 31, 2014	Feb. 28, 2014	Nov. 30, 2014	Oct. 31, 2014
Debt Instrument [Line Items]
Total fixed rate debt	$ 4,736,709,000					$ 4,130,629,000					$ 4,736,709,000		$ 4,130,629,000
Total floating rate debt	1,103,942,000					729,949,000					1,103,942,000		729,949,000
Total mortgages and other loans payable	5,840,651,000					4,860,578,000					5,840,651,000		4,860,578,000
Loss on early extinguishment of debt	(6,865,000)		(24,475,000)	(1,028,000)	3,000	5,000		0	(10,000)	(18,513,000)	(32,365,000)		(18,518,000)		(6,978,000)
1745 Broadway
Debt Instrument [Line Items]
Total fixed rate debt	16,000,000	[1]				0	[1]				16,000,000	[1]	0	[1]
388-390 Greenwich Street
Debt Instrument [Line Items]
Total fixed rate debt	1,004,000,000	[2]				0	[2]				1,004,000,000	[2]	0	[2]
Total floating rate debt	446,000,000	[2]				0	[2]				446,000,000	[2]	0	[2]
Joint venture
Debt Instrument [Line Items]
Total fixed rate debt	2,065,264,000					3,223,895,000					2,065,264,000		3,223,895,000
Total floating rate debt	1,713,440,000					1,842,815,000					1,713,440,000		1,842,815,000
Total mortgages and other loans payable	3,778,704,000					5,066,710,000					3,778,704,000		5,066,710,000
Maximum amount of loan recourse to entity	18,400,000										18,400,000
Joint venture | 7 Renaissance
Debt Instrument [Line Items]
Total fixed rate debt	2,147,000					1,276,000					2,147,000		1,276,000
Joint venture | 11 West 34th Street
Debt Instrument [Line Items]
Total fixed rate debt	16,905,000					17,205,000					16,905,000		17,205,000
Joint venture | 280 Park Avenue
Debt Instrument [Line Items]
Total fixed rate debt	700,171,000					706,886,000					700,171,000		706,886,000
Joint venture | 1745 Broadway
Debt Instrument [Line Items]
Total fixed rate debt	340,000,000					340,000,000					340,000,000		340,000,000
Joint venture | Jericho Plaza
Debt Instrument [Line Items]
Total fixed rate debt	163,750,000					163,750,000					163,750,000		163,750,000
Joint venture | 800 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	20,910,000					20,910,000					20,910,000		20,910,000
Joint venture | 315 West 36th Street
Debt Instrument [Line Items]
Total fixed rate debt	25,000,000					25,000,000					25,000,000		25,000,000
Joint venture | 521 Fifth Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)																		3.73%
Total fixed rate debt	170,000,000	[3]				0	[3]				170,000,000	[3]	0	[3]
Total floating rate debt	0	[3]				170,000,000	[3]				0	[3]	170,000,000	[3]
Joint venture | 717 Fifth Avenue | Mortgage loan
Debt Instrument [Line Items]
Committed amount	300,000,000										300,000,000
Joint venture | 717 Fifth Avenue | Mezzanine loans
Debt Instrument [Line Items]
Committed amount	290,000,000										290,000,000
Joint venture | 21 East 66th Street
Debt Instrument [Line Items]
Total fixed rate debt	12,000,000					12,000,000					12,000,000		12,000,000
Total floating rate debt	1,883,000					1,959,000					1,883,000		1,959,000
Joint venture | 388-390 Greenwich Street
Debt Instrument [Line Items]
Total fixed rate debt	0	[4]				996,082,000	[4]				0	[4]	996,082,000	[4]
Total floating rate debt	0	[4]				142,297,000	[4]				0	[4]	142,297,000	[4]
Loss on early extinguishment of debt																(2,400,000)
Joint venture | 100 Park Avenue
Debt Instrument [Line Items]
Total fixed rate debt	0	[5]				209,786,000	[5]				0	[5]	209,786,000	[5]
Total floating rate debt	360,000,000	[5]				0	[5]				360,000,000	[5]	0	[5]
Loss on early extinguishment of debt																	(3,200,000)
Joint venture | 21 West 34th Street
Debt Instrument [Line Items]
Total fixed rate debt	0	[6]				100,000,000	[6]				0	[6]	100,000,000	[6]
Joint venture | 1604-1610 Broadway
Debt Instrument [Line Items]
Total fixed rate debt	0	[7]				27,000,000	[7]				0	[7]	27,000,000	[7]
Incentive income											7,700,000
Joint venture | The Meadows
Debt Instrument [Line Items]
Total floating rate debt	67,350,000					67,350,000					67,350,000		67,350,000
Joint venture | 3 Columbus Circle
Debt Instrument [Line Items]
Total floating rate debt	230,974,000	[8]				239,233,000	[8]				230,974,000	[8]	239,233,000	[8]
Possible increase in mortgage based on meeting certain performance hurdles											40,000,000.0
Joint venture | 1552 Broadway
Debt Instrument [Line Items]
Total floating rate debt	184,210,000	[9]				158,690,000	[9]				184,210,000	[9]	158,690,000	[9]
Joint venture | 1552 Broadway | Mortgage loan
Debt Instrument [Line Items]
Committed amount	150,000,000										150,000,000
Unfunded amount	3,900,000										3,900,000
Joint venture | 1552 Broadway | Mezzanine loans
Debt Instrument [Line Items]
Committed amount	41,500,000										41,500,000
Unfunded amount	3,400,000										3,400,000
Joint venture | Other loan payable
Debt Instrument [Line Items]
Total floating rate debt	30,000,000					30,000,000					30,000,000		30,000,000
Joint venture | 650 Fifth Avenue
Debt Instrument [Line Items]
Total floating rate debt	65,000,000	[10]				0	[10]				65,000,000	[10]	0	[10]
Joint venture | 650 Fifth Avenue | Mortgage loan
Debt Instrument [Line Items]
Committed amount																			97,000,000
Unfunded amount																			32,000,000
Joint venture | 175-225 Third Street
Debt Instrument [Line Items]
Total floating rate debt	40,000,000					0					40,000,000		0
Joint venture | 10 East 53rd Street
Debt Instrument [Line Items]
Total floating rate debt	125,000,000					125,000,000					125,000,000		125,000,000
Joint venture | 724 Fifth Avenue
Debt Instrument [Line Items]
Total floating rate debt	275,000,000	[11]				120,000,000	[11]				275,000,000	[11]	120,000,000	[11]
Joint venture | 724 Fifth Avenue | Mezzanine loans
Debt Instrument [Line Items]
Loss on early extinguishment of debt											(1,200,000)
Joint venture | 33 Beekman
Debt Instrument [Line Items]
Total floating rate debt	52,283,000	[12]				18,362,000	[12]				52,283,000	[12]	18,362,000	[12]
Maximum amount of loan recourse to entity	75,000,000										75,000,000
Joint venture | 600 Lexington Avenue
Debt Instrument [Line Items]
Total floating rate debt	116,740,000					120,616,000					116,740,000		120,616,000
Joint venture | 55 West 46th Street
Debt Instrument [Line Items]
Total floating rate debt	150,000,000	[13]				0	[13]				150,000,000	[13]	0	[13]
Joint venture | 55 West 46th Street | Mortgage loan
Debt Instrument [Line Items]
Committed amount	190,000,000										190,000,000
Unfunded amount	40,000,000										40,000,000
Joint venture | 121 Greene Street
Debt Instrument [Line Items]
Total floating rate debt	15,000,000					0					15,000,000		0
Joint venture | 747 Madison Avenue
Debt Instrument [Line Items]
Total floating rate debt	0					33,125,000					0		33,125,000
Joint venture | West Coast office portfolio
Debt Instrument [Line Items]
Total floating rate debt	0	[14]				526,290,000	[14]				0	[14]	526,290,000	[14]
Joint venture | 180/182 Broadway
Debt Instrument [Line Items]
Total floating rate debt	0	[15]				89,893,000	[15]				0	[15]	89,893,000	[15]
Initial Maturity July 2022 | Joint venture | 717 Fifth Avenue
Debt Instrument [Line Items]
Total fixed rate debt	300,000,000	[16]				300,000,000	[16]				300,000,000	[16]	300,000,000	[16]
Initial Maturity July 2024 | Joint venture | 717 Fifth Avenue
Debt Instrument [Line Items]
Total fixed rate debt	$ 314,381,000	[16]				$ 304,000,000	[16]				$ 314,381,000	[16]	$ 304,000,000	[16]
Weighted Average | 1745 Broadway
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.81%	[1],[17]									4.81%	[1],[17]
Weighted Average | 388-390 Greenwich Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	2.99%	[17],[2]									2.99%	[17],[2]
Interest rate, floating rate debt (as a percent)	1.91%	[17],[2]									1.91%	[17],[2]
Weighted Average | Joint venture | 7 Renaissance
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	10.00%	[17]									10.00%	[17]
Weighted Average | Joint venture | 11 West 34th Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.82%	[17]									4.82%	[17]
Weighted Average | Joint venture | 280 Park Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	6.57%	[17]									6.57%	[17]
Weighted Average | Joint venture | 1745 Broadway
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.68%	[17]									5.68%	[17]
Weighted Average | Joint venture | Jericho Plaza
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.65%	[17]									5.65%	[17]
Weighted Average | Joint venture | 800 Third Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	6.00%	[17]									6.00%	[17]
Weighted Average | Joint venture | 315 West 36th Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.16%	[17]									3.16%	[17]
Weighted Average | Joint venture | 521 Fifth Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	2.48%	[17],[3]									2.48%	[17],[3]
Interest rate, floating rate debt (as a percent)	0.00%	[17],[3]									0.00%	[17],[3]
Weighted Average | Joint venture | 21 East 66th Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.60%	[17]									3.60%	[17]
Interest rate, floating rate debt (as a percent)	2.88%	[17]									2.88%	[17]
Weighted Average | Joint venture | 388-390 Greenwich Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	0.00%	[17],[4]									0.00%	[17],[4]
Interest rate, floating rate debt (as a percent)	0.00%	[17],[4]									0.00%	[17],[4]
Weighted Average | Joint venture | 100 Park Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	0.00%	[17],[5]									0.00%	[17],[5]
Interest rate, floating rate debt (as a percent)	2.36%	[17],[5]									2.36%	[17],[5]
Weighted Average | Joint venture | 21 West 34th Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	0.00%	[17],[6]									0.00%	[17],[6]
Weighted Average | Joint venture | 1604-1610 Broadway
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	0.00%	[17],[7]									0.00%	[17],[7]
Weighted Average | Joint venture | The Meadows
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	7.75%	[17]									7.75%	[17]
Weighted Average | Joint venture | 3 Columbus Circle
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.33%	[17],[8]									2.33%	[17],[8]
Weighted Average | Joint venture | 1552 Broadway
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	4.25%	[17],[9]									4.25%	[17],[9]
Weighted Average | Joint venture | Other loan payable
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.05%	[17]									1.05%	[17]
Weighted Average | Joint venture | 650 Fifth Avenue
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	3.66%	[10],[17]									3.66%	[10],[17]
Weighted Average | Joint venture | 175-225 Third Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	4.25%	[17]									4.25%	[17]
Weighted Average | Joint venture | 10 East 53rd Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.65%	[17]									2.65%	[17]
Weighted Average | Joint venture | 724 Fifth Avenue
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.57%	[11],[17]									2.57%	[11],[17]
Weighted Average | Joint venture | 33 Beekman
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.90%	[12],[17]									2.90%	[12],[17]
Weighted Average | Joint venture | 600 Lexington Avenue
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.23%	[17]									2.23%	[17]
Weighted Average | Joint venture | 55 West 46th Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.45%	[13],[17]									2.45%	[13],[17]
Weighted Average | Joint venture | 121 Greene Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.67%	[17]									1.67%	[17]
Weighted Average | Joint venture | 747 Madison Avenue
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	0.00%	[17]									0.00%	[17]
Weighted Average | Joint venture | West Coast office portfolio
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	0.00%	[14],[17]									0.00%	[14],[17]
Weighted Average | Joint venture | 180/182 Broadway
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	0.00%	[15],[17]									0.00%	[15],[17]
Weighted Average | Initial Maturity July 2022 | Joint venture | 717 Fifth Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.45%	[16],[17]									4.45%	[16],[17]
Weighted Average | Initial Maturity July 2024 | Joint venture | 717 Fifth Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	9.00%	[16],[17]									9.00%	[16],[17]

[1] In connection with our acquisition of Witkoff's interest in the unconsolidated joint venture which holds 1745 Broadway, we have assumed this partner loan.

[2] Simultaneous with the acquisition of our joint venture partner's interest, we refinanced the $1.1 billion floating rate mortgage with a $1.45 billion seven-year floating rate mortgage (including the as-of right extension option), and have consolidated the property. We assumed the existing derivative instruments, which swapped $504.0 million of the floating rate mortgage to a fixed rate mortgage which bears interest at 3.80% per annum. In October 2014, we entered into multiple swap agreements to hedge our interest rate exposure on the additional $500.0 million portion of this mortgage, which was swapped to a fixed rate of 2.69% per annum.

[3] This loan became a 3.73% fixed rate mortgage upon the effectivity of the interest rate swap in November 2014.

[4] In May 2014, we acquired the interest of our joint venture partner, thereby consolidating the entity. Simultaneous with the acquisition, we refinanced the mortgage and incurred a net loss on early extinguishment of debt of $2.4 million.

[5] In February 2014, the joint venture refinanced the previous mortgage and incurred a net loss on early extinguishment of debt of $3.2 million.

[6] In January 2014, we sold our interest in the joint venture, inclusive of our share of the joint venture debt.

[7] This loan was in default since November 2009 due to the non-payment of debt service. In January 2014, the joint venture surrendered its ground lease position to the lender. During the year ended December 31, 2014, we recognized $7.7 million of incentive income, which is included in other income on the consolidated statements of income.

[8] The joint venture has the ability to increase the mortgage by $40.0 million based on meeting certain performance hurdles. In connection with this obligation, we executed a master lease agreement and our joint venture partner executed a contribution agreement to reflect its pro rata obligation under the master lease. The lien on the mortgage and the master lease excludes the condominium interest owned by Y&R. See Note 4 of the first table.

[9] These loans are comprised of a $150.0 million mortgage loan and a $41.5 million mezzanine loan. As of December 31, 2014, $3.9 million of the mortgage loan and $3.4 million of the mezzanine loan remained unfunded.

[10] In October 2014, the joint venture closed on a $97.0 million leasehold mortgage, of which $32.0 million remained unfunded as of December 31, 2014.

[11] In April 2014, the joint venture refinanced the previous mortgage and incurred a net loss on early extinguishment of debt of $1.2 million.

[12] This loan has a committed amount of $75.0 million, of which $18.4 million is recourse to us. Our partner has indemnified us for its pro rata share of the recourse guarantee. A portion of the guarantee terminates upon the joint venture reaching certain milestones. We believe it is unlikely that we will be required to perform under this guarantee.

[13] This loan has a committed amount of $190.0 million, of which $40.0 million remained unfunded as of December 31, 2014.

[14] In March 2014, we sold our interest in the joint venture, inclusive of our share in the joint venture debt.

[15] In September 2014, the joint venture sold the property and repaid the debt.

[16] These loans are comprised of a $300.0 million fixed rate mortgage loan and $290.0 million mezzanine loan. The mezzanine loan is subject to accretion based on the difference between contractual interest rate and contractual pay rate.

[17] Effective weighted average interest rate for the year ended December 31, 2014, taking into account interest rate hedges in effect during the period.