Property Acquisitions (Details) - USD ($) $ in Thousands			1 Months Ended							3 Months Ended		9 Months Ended
	May. 15, 2014	May. 14, 2014	Aug. 31, 2015	Jul. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Oct. 31, 2014	Sep. 30, 2014	Jul. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Recognized Identifiable Assets Acquired and Liabilities Assumed
Impact to rental revenue for amortization of aggregate below-market leases										$ 318,465	$ 291,293	$ 926,020	$ 826,877
Impact to depreciation expense										146,185	94,443	454,087	274,337
Total fixed rate debt										5,824,875		5,824,875		$ 4,736,709
108 Broadway and 5 & 7 Dev Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land			$ 22,101
Building and building leasehold			41,045
Above market lease value			0
Acquired in-place leases			0
Other assets, net of other liabilities			0
Assets acquired			63,146
Mark-to-market assumed debt			0
Below market lease value			0
Derivatives			0
Liabilities assumed			0
Purchase price			63,146
Net consideration funded by us at closing, excluding consideration financed by debt			63,146
Equity and/or debt investment held			0
Debt assumed			0
108 Broadway and 5 & 7 Dev Street | Series R Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units										10,000		10,000
108 Broadway and 5 & 7 Dev Street | Series S Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units										$ 26,900		$ 26,900
11 Madison Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land			849,926
Building and building leasehold			1,579,118
Above market lease value			0
Acquired in-place leases			0
Other assets, net of other liabilities			0
Assets acquired			2,429,044
Mark-to-market assumed debt			0
Below market lease value			0
Derivatives			0
Liabilities assumed			0
Purchase price			2,429,044
Net consideration funded by us at closing, excluding consideration financed by debt			2,429,044
Equity and/or debt investment held			0
Debt assumed			$ 0
110 Greene Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				$ 89,250
Building and building leasehold				165,750
Above market lease value				0
Acquired in-place leases				0
Other assets, net of other liabilities				0
Assets acquired				255,000
Mark-to-market assumed debt				0
Below market lease value				0
Derivatives				0
Liabilities assumed				0
Purchase price				255,000
Net consideration funded by us at closing, excluding consideration financed by debt				255,000
Equity and/or debt investment held				0
Debt assumed				$ 0
Ownership interest in consolidated joint venture (as a percent)										90.00%		90.00%
110 Greene Street | Series P Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units										$ 5,000		$ 5,000
110 Greene Street | Series Q Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units										$ 6,700		6,700
Upper East Side Residential
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land					$ 17,500
Building and building leasehold					32,500
Above market lease value					0
Acquired in-place leases					0
Other assets, net of other liabilities					0
Assets acquired					50,000
Mark-to-market assumed debt					0
Below market lease value					0
Derivatives					0
Liabilities assumed					0
Purchase price					50,000
Net consideration funded by us at closing, excluding consideration financed by debt					50,000
Equity and/or debt investment held					0
Debt assumed					$ 0
Ownership interest in consolidated joint venture (as a percent)					95.10%
Upper East Side Residential | Series N Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units					$ 13,800
1640 Flatbush Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land						$ 6,120
Building and building leasehold						680
Above market lease value						0
Acquired in-place leases						0
Other assets, net of other liabilities						0
Assets acquired						6,800
Mark-to-market assumed debt						0
Below market lease value						0
Derivatives						0
Liabilities assumed						0
Purchase price						6,800
Net consideration funded by us at closing, excluding consideration financed by debt						6,800
Equity and/or debt investment held						0
Debt assumed						$ 0
102 Greene Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land							$ 8,215
Building and building leasehold							26,717
Above market lease value							0
Acquired in-place leases							1,015
Other assets, net of other liabilities							3
Assets acquired							35,950
Mark-to-market assumed debt							0
Below market lease value							3,701
Derivatives							0
Liabilities assumed							3,701
Purchase price							32,249
Net consideration funded by us at closing, excluding consideration financed by debt							32,249
Equity and/or debt investment held							0
Debt assumed							0
102 Greene Street | Scenario, Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land							11,300
Building and building leasehold							21,000
635 Madison Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land								$ 205,632			205,632		205,632
Building and building leasehold								15,805			15,805		15,805
Above market lease value								0			0		0
Acquired in-place leases								17,345			17,345		17,345
Other assets, net of other liabilities								0			0		0
Assets acquired								238,782			238,782		238,782
Mark-to-market assumed debt								0			0		0
Below market lease value								85,036			85,036		85,036
Derivatives								0			0		0
Liabilities assumed								85,036			85,036		85,036
Purchase price								153,746			153,746		153,746
Net consideration funded by us at closing, excluding consideration financed by debt								153,746
Equity and/or debt investment held								0
Debt assumed								0
635 Madison Avenue | Scenario, Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land								$ 153,700			$ 153,700		$ 153,700
719 Seventh Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land									$ 41,850
Building and building leasehold									0
Above market lease value									0
Acquired in-place leases									0
Other assets, net of other liabilities									0
Assets acquired									41,850
Mark-to-market assumed debt									0
Below market lease value									0
Derivatives									0
Liabilities assumed									0
Purchase price									41,850
Net consideration funded by us at closing, excluding consideration financed by debt									41,850
Equity and/or debt investment held									0
Debt assumed									$ 0
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
719 Seventh Avenue | Series K Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units									9,500
719 Seventh Avenue | Scenario, Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land									14,400
Building and building leasehold									26,700
115 Spring Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land									11,078
Building and building leasehold									44,799
Above market lease value									0
Acquired in-place leases									2,037
Other assets, net of other liabilities									0
Assets acquired									57,914
Mark-to-market assumed debt									0
Below market lease value									4,789
Derivatives									0
Liabilities assumed									4,789
Purchase price									53,125
Net consideration funded by us at closing, excluding consideration financed by debt									53,125
Equity and/or debt investment held									0
Debt assumed									0
115 Spring Street | Scenario, Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land									15,900
Building and building leasehold									$ 37,200
388-390 Greenwich Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land	$ 516,292
Building and building leasehold	964,434
Above market lease value	0
Acquired in-place leases	302,430
Other assets, net of other liabilities	6,495
Assets acquired	1,789,651
Mark-to-market assumed debt	0
Below market lease value	186,782
Derivatives	18,001
Liabilities assumed	204,783
Purchase price	1,584,868	$ 1,585,000
Net consideration funded by us at closing, excluding consideration financed by debt	208,614	208,614
Equity and/or debt investment held	148,025	148,025
Debt assumed	$ 1,162,379	1,162,379
Economic interest (as a percent)	49.65%
Value of interest	$ 1,585,000
Face amount of loan	1,450,000
Notional value	504,000
Total fixed rate debt							$ 500,000
Purchase price fair value adjustment	71,400	$ 71,446
388-390 Greenwich Street | Scenario, Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land	558,700
Building and building leasehold	$ 1,000,000
102 Greene Street, 635 Madison Avenue, 719 Seventh Avenue, 115 Spring Street, and 388-390 Greenwich Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Impact to rental revenue for amortization of aggregate below-market leases												7,600
Impact to depreciation expense												$ 10,300