Fair Value Measurements (Details) - Related Party Transactions By Transaction [Domain] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	$ 39,931	$ 44,646
Short-term Investments	0	24,998
Interest rate cap (included in other assets)	1	11
Total assets	39,932	69,655
Liabilities measured at fair value	0	0
Carrying Reported Amount Fair Value Disclosure [Member]
Assets
Cash Equivalents	185,523	111,590
Liabilities
Mortgages Payable	1,031,213	1,032,780
Leasing commissions (included in amounts due to Vornado)	8	0
Total liabilities not measured at fair value	1,031,221	1,032,780
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets
Cash Equivalents	185,523	111,590
Liabilities
Mortgages Payable	1,020,000	1,025,000
Leasing commissions (included in amounts due to Vornado)	8	0
Total liabilities not measured at fair value	1,020,008	1,025,000
Fair Value, Inputs, Level 1 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	39,931	44,646
Short-term Investments		24,998
Interest rate cap (included in other assets)	0	0
Total assets	39,931	69,644
Fair Value, Inputs, Level 2 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	0	0
Short-term Investments		0
Interest rate cap (included in other assets)	1	11
Total assets	1	11
Fair Value, Inputs, Level 3 [Member]
Financial Assets And Liabilities Measured At Fair Value
Marketable securities	0	0
Short-term Investments		0
Interest rate cap (included in other assets)	0	0
Total assets	$ 0	$ 0