Investment in Unconsolidated Joint Ventures (Details 2) (USD $)	3 Months Ended			9 Months Ended					9 Months Ended																																9 Months Ended				1 Months Ended									9 Months Ended							9 Months Ended				9 Months Ended																	9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013	Dec. 31, 2013		Sep. 30, 2014 388 and 390 Greenwich Street		Dec. 31, 2013 388 and 390 Greenwich Street		Sep. 30, 2014 Joint Venture	Dec. 31, 2013 Joint Venture	Sep. 30, 2014 Joint Venture 7 Renaissance		Dec. 31, 2013 Joint Venture 7 Renaissance	Sep. 30, 2014 Joint Venture 11 West 34th Street		Dec. 31, 2013 Joint Venture 11 West 34th Street	Sep. 30, 2014 Joint Venture 280 Park Avenue		Dec. 31, 2013 Joint Venture 280 Park Avenue	Sep. 30, 2014 Joint Venture 1745 Broadway		Dec. 31, 2013 Joint Venture 1745 Broadway	Sep. 30, 2014 Joint Venture 1 and 2 Jericho Plaza		Dec. 31, 2013 Joint Venture 1 and 2 Jericho Plaza	Sep. 30, 2014 Joint Venture 800 Third Avenue		Dec. 31, 2013 Joint Venture 800 Third Avenue	Sep. 30, 2014 Joint Venture 315 West 36th Street		Dec. 31, 2013 Joint Venture 315 West 36th Street	Sep. 30, 2014 Joint Venture 717 Fifth Avenue Mortgage loan	Sep. 30, 2014 Joint Venture 717 Fifth Avenue Mezzanine loans	Sep. 30, 2014 Joint Venture 21 East 66th Street		Dec. 31, 2013 Joint Venture 21 East 66th Street	Sep. 30, 2014 Joint Venture 388 and 390 Greenwich Street		Dec. 31, 2013 Joint Venture 388 and 390 Greenwich Street		Feb. 28, 2014 Joint Venture 100 Park Avenue	Sep. 30, 2014 Joint Venture 100 Park Avenue		Dec. 31, 2013 Joint Venture 100 Park Avenue		Sep. 30, 2014 Joint Venture 21 West 34th Street		Dec. 31, 2013 Joint Venture 21 West 34th Street		Sep. 30, 2014 Joint Venture 1604-1610 Broadway		Dec. 31, 2013 Joint Venture 1604-1610 Broadway		Sep. 30, 2014 Joint Venture The Meadows		Dec. 31, 2013 Joint Venture The Meadows	Sep. 30, 2014 Joint Venture 3 Columbus Circle		Dec. 31, 2013 Joint Venture 3 Columbus Circle		Sep. 30, 2014 Joint Venture 1552 Broadway extension		Dec. 31, 2013 Joint Venture 1552 Broadway		Sep. 30, 2014 Joint Venture 1552 Broadway Mortgage loan	Sep. 30, 2014 Joint Venture 1552 Broadway Mezzanine loans	Sep. 30, 2014 Joint Venture Other loan payable		Dec. 31, 2013 Joint Venture Other loan payable	Sep. 30, 2014 Joint Venture 10 East 53rd Street		Dec. 31, 2013 Joint Venture 10 East 53rd Street	Sep. 30, 2014 Joint Venture 724 Fifth Avenue		Dec. 31, 2013 Joint Venture 724 Fifth Avenue		Apr. 30, 2014 Joint Venture 724 Fifth Avenue Mortgage loan	Sep. 30, 2014 Joint Venture 724 Fifth Avenue Mezzanine loans	Apr. 30, 2014 Joint Venture 724 Fifth Avenue Mezzanine loans	Sep. 30, 2014 Joint Venture 33 Beekman		Dec. 31, 2013 Joint Venture 33 Beekman		Sep. 30, 2014 Joint Venture 600 Lexington Avenue		Dec. 31, 2013 Joint Venture 600 Lexington Avenue	Sep. 30, 2014 Joint Venture 521 Fifth Avenue		Dec. 31, 2013 Joint Venture 521 Fifth Avenue	Sep. 30, 2014 Joint Venture 747 Madison Avenue		Dec. 31, 2013 Joint Venture 747 Madison Avenue	Sep. 30, 2014 Joint Venture West Coast office portfolio		Dec. 31, 2013 Joint Venture West Coast office portfolio		Sep. 30, 2014 Joint Venture 180/182 Broadway		Dec. 31, 2013 Joint Venture 180/182 Broadway		Sep. 30, 2014 Joint Venture Initial Maturity July 2022 717 Fifth Avenue		Dec. 31, 2013 Joint Venture Initial Maturity July 2022 717 Fifth Avenue		Sep. 30, 2014 Joint Venture Initial Maturity July 2024 717 Fifth Avenue		Dec. 31, 2013 Joint Venture Initial Maturity July 2024 717 Fifth Avenue
Mortgages and Other Loans Payable
Interest rate, fixed rate debt (as a percent)									3.80%	[1],[2]					10.00%	[2]		4.82%	[2]		6.57%	[2]		5.68%	[2]		5.65%	[2]		6.00%	[2]		3.16%	[2]				3.60%	[2]		0.00%	[2],[3]				0.00%	[4]			0.00%	[5]			0.00%	[2],[6]																																																		4.45%	[2],[7]			9.00%	[2],[7]
Total fixed rate debt	$ 4,732,032,000			$ 4,732,032,000			$ 4,130,629,000		$ 504,000,000	[1]	$ 0	[1]	$ 1,894,136,000	$ 3,223,895,000	$ 1,868,000		$ 1,276,000	$ 16,982,000		$ 17,205,000	$ 701,928,000		$ 706,886,000	$ 340,000,000		$ 340,000,000	$ 163,750,000		$ 163,750,000	$ 20,910,000		$ 20,910,000	$ 25,000,000		$ 25,000,000			$ 12,000,000		$ 12,000,000	$ 0	[3]	$ 996,082,000	[3]		$ 0	[4]	$ 209,786,000	[4]	$ 0	[5]	$ 100,000,000	[5]	$ 0	[6]	$ 27,000,000	[6]																																																$ 300,000,000	[7]	$ 300,000,000	[7]	$ 311,698,000	[7]	$ 304,000,000	[7]
Interest rate, floating rate debt (as a percent)									1.91%	[1],[2]																												2.88%	[2]		0.00%	[2],[3]				1.91%	[2],[4]											7.75%	[2]		2.34%	[2],[8]			4.21%	[2],[9]					1.06%	[2]		2.66%	[2]		2.58%	[10],[2]						2.91%	[11],[2]			2.24%	[2]		2.36%	[2]		0.00%	[2]		0.00%	[12],[2]			0.00%	[13],[2]
Total floating rate debt	1,606,152,000			1,606,152,000			729,949,000		946,000,000	[1]	0	[1]	1,604,619,000	1,842,815,000																								1,902,000		1,959,000	0	[3]	142,297,000	[3]		360,000,000	[4]	0	[4]									67,350,000		67,350,000	233,058,000	[8]	239,233,000	[8]	180,885,000	[9]	158,690,000	[9]			30,000,000		30,000,000	125,000,000		125,000,000	275,000,000	[10]	120,000,000	[10]				43,707,000	[11]	18,362,000	[11]	117,717,000		120,616,000	170,000,000		170,000,000	0		33,125,000	0	[12]	526,290,000	[12]	0	[13]	89,893,000	[13]
Mortgages and other loans payable	6,338,184,000	[14]		6,338,184,000	[14]		4,860,578,000	[14]					3,498,755,000	5,066,710,000
Committed amount																																				300,000,000	290,000,000																																150,000,000	41,500,000
Loss on early extinguishment of debt	24,475,000		0	25,500,000		18,523,000																																			2,400,000				3,200,000																																					1,200,000
Face amount of loan									1,500,000,000																																				360,000,000																																				235,000,000		40,000,000
Term of refinanced mortgage									7 years																																				7 years
Incentive income																																																						7,700,000
Possible increase in mortgage based on meeting certain performance hurdles																																																													40,000,000.0
Number of extension options (extensions)																																																																	2
Period of extension option for mortgage secured by the portfolio																																																																	1 year
Unfunded amount																																																																					5,700,000	4,900,000
Maximum amount of loan recourse to entity																																																																																				$ 75,000,000

[1] Simultaneous with the acquisition of our joint venture partner's interest, we refinanced the $1.1 billion floating rate mortgage with a $1.5 billion seven-year floating rate mortgage, and have consolidated the property.

[2] Effective weighted average interest rate for the three months ended September 30, 2014, taking into account interest rate hedges in effect during the period.

[3] In May 2014, we acquired the interest of our joint venture 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.

[4] In February 2014, the joint venture replaced the previous fixed rate mortgage with a $360.0 million, seven-year floating rate, mortgage and incurred a net loss on early extinguishment of $3.2 million.

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

[6] This loan was in default since November 2009 due to the non-payment of debt service. In January 2014, the joint venture relinquished its ground lease position to the lender. During the nine months ended September 30, 2014, we recognized $7.7 million of incentive income, which is included in other income on the consolidated statements of income.

[7] 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.

[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 2 of prior table.

[9] These loans are comprised of a $150.0 million mortgage loan and a $41.5 million mezzanine loan and are subject to two one-year extension options. As of September 30, 2014, $5.7 million of the mortgage loan and $4.9 million of the mezzanine loan remained unfunded.

[10] In April 2014, the joint venture refinanced the previous mortgage with a $235.0 million mortgage and a $40.0 million mezzanine loan and incurred a net loss on early extinguishment of debt of $1.2 million.

[11] This loan has a committed amount of $75.0 million, which 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.

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

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

[14] Includes mortgages related to 2 Herald Square and 180 Maiden, which are currently held for sale.