Commitments and Contingencies (Details Textual)	9 Months Ended
	Sep. 30, 2015 USD ($) Number	Dec. 31, 2014 USD ($)
Commitments and Contingencies (Textual) [Abstract]
Number of outstanding letters of credit | Number	8
Letter of credit obligation	$ 73,655,000
Line Of Credit Facility [Line Items]
Outstanding construction financings for leased properties	197,639,000	$ 186,327,000
Additional financing to complete construction	408,372,000
Total contingent purchase obligations	$ 29,427,000
Minimum part of economic life of the leased asset to be classified as capital lease	75.00%
Minimum net present value of the future minimum lease payments to be classified as capital lease.	90.00%
Operating lease obligations relating to certain ground leases	$ 988,564,000
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	27,126,000
Capital Leases, Future Minimum Payments Due	99,751,000
Purchase Obligation for Acquisitions Expected to be Completed before YE	$ 236,068,000
Letter Of Credit Expiration Date Maximum	Dec. 31, 2018
Letter Of Credit Expiration Date Minimum	Jan. 01, 2015