Acquisitions Acquisitions - Schedule of allocation of the purchase price for assets and liabilities acquired (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended	9 Months Ended
	Jul. 15, 2014	Sep. 30, 2014	Sep. 30, 2013	Jul. 15, 2014
Consideration paid:
Cash and issuance of Class A Common Stock, Class B Common Stock, and Series PR OP units	$ 565,916
Debt assumed	167,684	182,851	0
Total consideration paid	733,600
Net assets acquired:
Land and building and improvements				356,206
Acquired below-market ground leases				333,046
Acquired above-market leases				13,048
Acquired in place lease value and deferred leasing costs				88,080
Mortgage notes payable, inclusive of premium				(182,851)
Acquired below-market leases				(36,458)
Other liabilities, net of other assets				(5,155)
Total net assets acquired				$ 565,916