Mortgages and Other Loans Payable (Details) (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	Sep. 30, 2014	Feb. 28, 2013	Dec. 31, 2014		Jun. 30, 2014	Apr. 30, 2014	Nov. 30, 2012	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					$ 4,736,709,000
Total floating rate debt	1,103,942,000					729,949,000					1,103,942,000		729,949,000					1,103,942,000
Total mortgages and other loans payable	5,840,651,000					4,860,578,000					5,840,651,000		4,860,578,000					5,840,651,000
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
Junior subordinate deferrable interest debentures held by trusts																						1,600,000,000.0
Book value of collateral	8,200,000,000					8,000,000,000					8,200,000,000		8,000,000,000					8,200,000,000
Series J Preferred Stock
Debt Instrument [Line Items]
Total fixed rate debt	4,000,000	[1]				0	[1]				4,000,000	[1]	0	[1]				4,000,000	[1]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	4,000,000										4,000,000							4,000,000
Preferred Units, shares outstanding (shares)	4,000										4,000							4,000
Preferred Units (as a percent)											3.75%
Preferred Units, liquidation preference (in dollars per share)	$ 1,000.00										$ 1,000.00							$ 1,000.00
Master repurchase
Debt Instrument [Line Items]
Total floating rate debt	100,000,000	[2]				91,000,000	[2]				100,000,000	[2]	91,000,000	[2]				100,000,000	[2]
711 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	120,000,000					120,000,000					120,000,000		120,000,000					120,000,000
500 West Putnam Avenue
Debt Instrument [Line Items]
Total fixed rate debt	22,968,000					23,529,000					22,968,000		23,529,000					22,968,000
Landmark Square
Debt Instrument [Line Items]
Total fixed rate debt	81,269,000					82,909,000					81,269,000		82,909,000					81,269,000
485 Lexington Avenue
Debt Instrument [Line Items]
Total fixed rate debt	450,000,000					450,000,000					450,000,000		450,000,000					450,000,000
120 West 45th Street
Debt Instrument [Line Items]
Total fixed rate debt	170,000,000					170,000,000					170,000,000		170,000,000					170,000,000
762 Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt	8,045,000					8,211,000					8,045,000		8,211,000					8,045,000
885 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	267,650,000					267,650,000					267,650,000		267,650,000					267,650,000
1745 Broadway
Debt Instrument [Line Items]
Total fixed rate debt	16,000,000	[3]				0	[3]				16,000,000	[3]	0	[3]				16,000,000	[3]
388-390 Greenwich Street
Debt Instrument [Line Items]
Total fixed rate debt	1,004,000,000	[4]				0	[4]				1,004,000,000	[4]	0	[4]				1,004,000,000	[4]
Total floating rate debt	446,000,000	[4]				0	[4]				446,000,000	[4]	0	[4]				446,000,000	[4]
Extinguishment of debt											1,100,000,000
Refinanced mortgage loan	1,450,000,000										1,450,000,000							1,450,000,000
Term											7 years
388-390 Greenwich Street | Swap One
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.80%										3.80%							3.80%
Total fixed rate debt	504,000,000										504,000,000							504,000,000
388-390 Greenwich Street | Swap Two
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)																							2.69%
Total fixed rate debt																							500,000,000
One Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt	565,742,000					587,336,000					565,742,000		587,336,000					565,742,000
100 Church
Debt Instrument [Line Items]
Total fixed rate debt	228,612,000					230,000,000					228,612,000		230,000,000					228,612,000
919 Third Avenue
Debt Instrument [Line Items]
Total fixed rate debt	500,000,000	[5]				500,000,000	[5]				500,000,000	[5]	500,000,000	[5]				500,000,000	[5]
Interest in property (as a percent)	51.00%										51.00%							51.00%
400 East 57th Street
Debt Instrument [Line Items]
Total fixed rate debt	68,896,000					70,000,000					68,896,000		70,000,000					68,896,000
400 East 58th Street
Debt Instrument [Line Items]
Total fixed rate debt	29,527,000					30,000,000					29,527,000		30,000,000					29,527,000
420 Lexington Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.99%										3.99%							3.99%
Total fixed rate debt	300,000,000	[6]				182,641,000	[6]				300,000,000	[6]	182,641,000	[6]				300,000,000	[6]
Loss on early extinguishment of debt																24,500,000
1515 Broadway
Debt Instrument [Line Items]
Total fixed rate debt	900,000,000	[7]				900,000,000	[7]				900,000,000	[7]	900,000,000	[7]				900,000,000	[7]
Loss on early extinguishment of debt																	18,500,000
Other loan payable
Debt Instrument [Line Items]
Total fixed rate debt	0	[8]				50,000,000	[8]				0	[8]	50,000,000	[8]				0	[8]
609 Partners, LLC
Debt Instrument [Line Items]
Total fixed rate debt	0	[9]				23,000	[9]				0	[9]	23,000	[9]				0	[9]
609 Partners, LLC | Series E preferred units
Debt Instrument [Line Items]
Preferred Units, shares outstanding (shares)																					22,658
125 Park Avenue
Debt Instrument [Line Items]
Total fixed rate debt	0	[10]				146,250,000	[10]				0	[10]	146,250,000	[10]				0	[10]
2 Herald Square
Debt Instrument [Line Items]
Total fixed rate debt	0	[11]				191,250,000	[11]				0	[11]	191,250,000	[11]				0	[11]
625 Madison Avenue
Debt Instrument [Line Items]
Total fixed rate debt	0					120,830,000					0		120,830,000					0
Loss on early extinguishment of debt																		6,900,000
Master repurchase
Debt Instrument [Line Items]
Junior subordinate deferrable interest debentures held by trusts	300,000,000.0										300,000,000.0							300,000,000.0
180 Maiden Lane
Debt Instrument [Line Items]
Total floating rate debt	253,942,000	[12]				262,706,000	[12]				253,942,000	[12]	262,706,000	[12]				253,942,000	[12]
248-252 Bedford Avenue
Debt Instrument [Line Items]
Total floating rate debt	29,000,000	[13]				22,000,000	[13]				29,000,000	[13]	22,000,000	[13]				29,000,000	[13]
Loss on early extinguishment of debt																				500,000
220 East 42nd Street
Debt Instrument [Line Items]
Total floating rate debt	275,000,000					275,000,000					275,000,000		275,000,000					275,000,000
16 Court Street
Debt Instrument [Line Items]
Total floating rate debt	0	[14]				79,243,000	[14]				0	[14]	79,243,000	[14]				0	[14]
Loss on early extinguishment of debt																					$ 500,000
Weighted Average | Series J Preferred Stock
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.75%	[1],[15]									3.75%	[1],[15]						3.75%	[1],[15]
Weighted Average | Master repurchase
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	3.38%	[15],[2]									3.38%	[15],[2]						3.38%	[15],[2]
Weighted Average | 711 Third Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.99%	[15]									4.99%	[15]						4.99%	[15]
Weighted Average | 500 West Putnam Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.52%	[15]									5.52%	[15]						5.52%	[15]
Weighted Average | Landmark Square
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.00%	[15]									4.00%	[15]						4.00%	[15]
Weighted Average | 485 Lexington Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.61%	[15]									5.61%	[15]						5.61%	[15]
Weighted Average | 120 West 45th Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	6.12%	[15]									6.12%	[15]						6.12%	[15]
Weighted Average | 762 Madison Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.75%	[15]									3.75%	[15]						3.75%	[15]
Weighted Average | 885 Third Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	6.26%	[15]									6.26%	[15]						6.26%	[15]
Weighted Average | 1745 Broadway
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.81%	[15],[3]									4.81%	[15],[3]						4.81%	[15],[3]
Weighted Average | 388-390 Greenwich Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	2.99%	[15],[4]									2.99%	[15],[4]						2.99%	[15],[4]
Interest rate, floating rate debt (as a percent)	1.91%	[15],[4]									1.91%	[15],[4]						1.91%	[15],[4]
Weighted Average | One Madison Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.91%	[15]									5.91%	[15]						5.91%	[15]
Weighted Average | 100 Church
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.68%	[15]									4.68%	[15]						4.68%	[15]
Weighted Average | 919 Third Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.12%	[15],[5]									5.12%	[15],[5]						5.12%	[15],[5]
Weighted Average | 400 East 57th Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.13%	[15]									4.13%	[15]						4.13%	[15]
Weighted Average | 400 East 58th Street
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	4.13%	[15]									4.13%	[15]						4.13%	[15]
Weighted Average | 420 Lexington Avenue
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	5.95%	[15],[6]									5.95%	[15],[6]						5.95%	[15],[6]
Weighted Average | 1515 Broadway
Debt Instrument [Line Items]
Interest rate, fixed rate debt (as a percent)	3.93%	[15],[7]									3.93%	[15],[7]						3.93%	[15],[7]
Weighted Average | 180 Maiden Lane
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	2.35%	[12],[15]									2.35%	[12],[15]						2.35%	[12],[15]
Weighted Average | 248-252 Bedford Avenue
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.93%	[13],[15]									1.93%	[13],[15]						1.93%	[13],[15]
Weighted Average | 220 East 42nd Street
Debt Instrument [Line Items]
Interest rate, floating rate debt (as a percent)	1.75%	[15]									1.75%	[15]						1.75%	[15]

[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] The Master Repurchase Agreement, or MRA, has a maximum facility capacity of $300.0 million. In December 2014, we extended the maturity date of the MRA to December 5, 2015.

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

[4] 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.

[5] We own a 51.0% controlling interest in the joint venture that is the borrower on this loan.

[6] In September 2014, we refinanced the previous mortgage and incurred a loss on early extinguishment of debt of $24.5 million. The new loan bears a fixed interest rate of 3.99% per annum.

[7] In February 2013, we refinanced the mortgage and incurred a loss on early extinguishment of debt of $18.5 million.

[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] In April 2014, the remaining 22,658 Series E Preferred Units of the Operating Partnership were canceled.

[10] In October 2014, we repaid the loan at maturity.

[11] In December 2014, we prepaid the loan and incurred a loss on early extinguishment of debt of $6.9 million.

[12] In connection with this consolidated joint venture obligation, we executed a master lease agreement. Our partner has executed a contribution agreement to reflect its pro rata share of the obligation under the master lease. This property was held for sale at December 31, 2014 and the related mortgage is included in liabilities related to assets held for sale. In January 2015, the property was sold and the debt was repaid.

[13] In June 2014, we refinanced the mortgage and incurred a loss on early extinguishment of debt of $0.5 million. In April 2014, we repaid the mortgage and incurred a loss on early extinguishment of debt of $0.5 million.

[14] il 2014, we repaid the mortgage and incurred a loss on early extinguishment of de

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