Property Acquisitions (Details) (USD $)	3 Months Ended		1 Months Ended		0 Months Ended		1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Jul. 31, 2014	May 15, 2014	May 14, 2014	May 31, 2014
Recognized Identifiable Assets Acquired and Liabilities Assumed
Impact to rental revenue for amortization of aggregate below-market leases	$ 303,329,000	$ 255,976,000
Impact to depreciation expense	108,337,000	86,515,000
1640 Flatbush Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land	6,120,000		6,120,000
Building and building leasehold	680,000		680,000
Above market lease value	0		0
Acquired in-place leases	0		0
Other assets, net of other liabilities	0		0
Assets acquired	6,800,000		6,800,000
Mark-to-market assumed debt	0		0
Below market lease value	0		0
Derivatives	0		0
Liabilities assumed	0		0
Purchase price	6,800,000		6,800,000
Net consideration funded by us at closing, excluding consideration financed by debt			6,800,000
Equity and/or debt investment held			0
Debt assumed			0
719 Seventh Avenue
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				41,850,000
Building and building leasehold				0
Above market lease value				0
Acquired in-place leases				0
Other assets, net of other liabilities				0
Assets acquired				41,850,000
Mark-to-market assumed debt				0
Below market lease value				0
Derivatives				0
Liabilities assumed				0
Purchase price				41,850,000
Net consideration funded by us at closing, excluding consideration financed by debt				41,850,000
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				14,100,000
719 Seventh Avenue | Series K Preferred Units
Recognized Identifiable Assets Acquired and Liabilities Assumed
Issuance of aggregate liquidation preference of preferred units				9,500,000
719 Seventh Avenue | Scenario, Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				14,400,000
Building and building leasehold				26,700,000
115 Spring Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				11,078,000
Building and building leasehold				44,799,000
Above market lease value				0
Acquired in-place leases				2,037,000
Other assets, net of other liabilities				0
Assets acquired				57,914,000
Mark-to-market assumed debt				0
Below market lease value				4,789,000
Derivatives				0
Liabilities assumed				4,789,000
Purchase price				53,125,000
Net consideration funded by us at closing, excluding consideration financed by debt				53,125,000
Equity and/or debt investment held				0
Debt assumed				0
115 Spring Street | Scenario, Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land				15,900,000
Building and building leasehold				37,200,000
388-390 Greenwich Street
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land					516,292,000
Building and building leasehold					964,434,000
Above market lease value					0
Acquired in-place leases					302,430,000
Other assets, net of other liabilities					6,495,000
Assets acquired					1,789,651,000
Mark-to-market assumed debt					0
Below market lease value					186,782,000
Derivatives					18,001,000
Liabilities assumed					204,783,000
Purchase price					1,584,868,000	1,585,000,000
Net consideration funded by us at closing, excluding consideration financed by debt					208,614,000	208,614,000
Equity and/or debt investment held					148,025,000	148,025,000
Debt assumed					1,162,379,000	1,162,379,000
Economic interest (as a percent)							49.65%
Value of interest							1,585,000,000
Face amount of loan							1,450,000,000
Notional value							504,000,000
Purchase price fair value adjustment						71,446,000	71,400,000
388-390 Greenwich Street | Scenario, Previously Reported
Recognized Identifiable Assets Acquired and Liabilities Assumed
Land							558,700,000
Building and building leasehold							1,000,000,000
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	6,700,000
Impact to depreciation expense	$ 10,100,000