Property Acquisitions - Additional Information (Details) - USD ($) $ in Thousands		1 Months Ended						12 Months Ended
	Nov. 30, 2015	Mar. 31, 2016	Dec. 31, 2015	Aug. 31, 2015	Jul. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2017	Jun. 30, 2016
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units								$ 221,932	$ 221,932
Impact to rental revenue for amortization of aggregate below-market leases								1,100,993	1,323,767	$ 1,245,981
Impact to depreciation expense								403,320	821,041	$ 560,887
600 Lexington Ave | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land									97,000
Building and building leasehold									$ 180,200
183 Broadway
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land											$ 5,799
Building and building leasehold											23,431
Above market lease value											0
Acquired in-place leases											773
Other assets, net of other liabilities											20
Assets acquired											30,023
Mark-to-market assumed debt											0
Below market lease value											(1,523)
Derivatives											0
Liabilities assumed											(1,523)
Purchase price											$ 28,500
Net consideration funded by us at closing, excluding consideration financed by debt		$ 28,500
Equity and/or debt investment held		0
Debt assumed		0
600 Lexington Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land								81,670
Building and building leasehold								182,447
Above market lease value								3,320
Acquired in-place leases								22,449
Other assets, net of other liabilities								0
Assets acquired								289,886
Mark-to-market assumed debt								(55)
Below market lease value								(5,831)
Derivatives								0
Liabilities assumed								(5,886)
Purchase price	$ 284,000							$ 284,000
Net consideration funded by us at closing, excluding consideration financed by debt	79,085		$ 79,085
Equity and/or debt investment held	54,575		54,575
Debt assumed	112,795		112,795
Ownership interest in consolidated joint venture (as a percent)								45.00%
Value of interest								$ 277,300
Purchase price fair value adjustment	$ 40,078		$ 40,100
183, 187 Broadway & 5-7 Dey Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				$ 20,266
Building and building leasehold				42,468
Above market lease value				17
Acquired in-place leases				3,621
Other assets, net of other liabilities				0
Assets acquired				66,372
Mark-to-market assumed debt				0
Below market lease value				(3,226)
Derivatives				0
Liabilities assumed				(3,226)
Purchase price				63,146
Net consideration funded by us at closing, excluding consideration financed by debt				0
Equity and/or debt investment held				0
Debt assumed				0
183, 187 Broadway & 5-7 Dey Street | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				22,100
Building and building leasehold				41,000
183, 187 Broadway & 5-7 Dey Street | Series R Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units								10,000
183, 187 Broadway & 5-7 Dey Street | Series S Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units								$ 26,900
11 Madison Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				675,776
Building and building leasehold				1,553,602
Above market lease value				19,764
Acquired in-place leases				366,949
Other assets, net of other liabilities				0
Assets acquired				2,616,091
Mark-to-market assumed debt				0
Below market lease value				(187,732)
Derivatives				0
Liabilities assumed				(187,732)
Purchase price				2,428,359
Net consideration funded by us at closing, excluding consideration financed by debt				0
Equity and/or debt investment held				0
Debt assumed				0
11 Madison Avenue | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				849,900
Building and building leasehold				$ 1,600,000
110 Greene Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land					$ 45,120
Building and building leasehold					215,470
Above market lease value					0
Acquired in-place leases					8,967
Other assets, net of other liabilities					0
Assets acquired					269,557
Mark-to-market assumed debt					0
Below market lease value					(14,557)
Derivatives					0
Liabilities assumed					(14,557)
Purchase price					255,000
Net consideration funded by us at closing, excluding consideration financed by debt					0
Equity and/or debt investment held					0
Debt assumed					$ 0
Ownership interest in consolidated joint venture (as a percent)					90.00%
110 Greene Street | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land					$ 89,300
Building and building leasehold					165,800
110 Greene Street | Series P Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units					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
Upper East Side Residential
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land												$ 48,152
Building and building leasehold												0
Above market lease value												0
Acquired in-place leases												1,922
Other assets, net of other liabilities												0
Assets acquired												50,074
Mark-to-market assumed debt												0
Below market lease value												0
Derivatives												0
Liabilities assumed												0
Purchase price												$ 50,074
Net consideration funded by us at closing, excluding consideration financed by debt						$ 0
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		6,226
Building and building leasehold		501
Above market lease value		0
Acquired in-place leases		146
Other assets, net of other liabilities		0
Assets acquired		6,873
Mark-to-market assumed debt		0
Below market lease value		(73)
Derivatives		0
Liabilities assumed		(73)
Purchase price		6,800
Net consideration funded by us at closing, excluding consideration financed by debt							$ 0
Equity and/or debt investment held							0
Debt assumed							$ 0
1640 Flatbush Avenue | As Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land		6,100
Building and building leasehold		$ 700