Acquisitions Schedule of allocation of the purchase price for assets and liabilities acquired (Details) (USD $) In Thousands, unless otherwise specified		0 Months Ended
	Dec. 31, 2013	Oct. 06, 2013 Total Acquisitions [Member]	Oct. 06, 2013 Leasehold Positions [Member]	Oct. 06, 2013 1333 Broadway Associates [Member]	Oct. 06, 2013 1350 Broadway Associates [Member]
Consideration paid:
Cash and issuance of Class A Common Stock, Class B Common Stock, and OP units		$ 1,047,487
Debt assumed		124,354
Total consideration paid		1,171,841
Net assets acquired:
Land		91,435
Building and improvements		516,344
Acquired below-market ground lease		62,738
Acquired above-market leases		72,123
Acquired in place lease value and deferred leasing costs		186,415
Goodwill	491,479	491,479
Other assets, net of other liabilities		6,061
Mortgage notes payable		(136,226)
Acquired below-market leases		(134,651)
Total purchase price allocated		1,155,718
Business Combination, Bargain Purchase [Abstract]
Total		$ 108,231	$ 35,147	$ 40,962	$ 32,122