Commitments and Contingencies (Details Textual)	6 Months Ended
	Jun. 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	$ 75,553,000
Outstanding construction financings for leased properties	159,352,000	$ 186,327,000
Additional financing to complete construction	402,894,000
Total contingent purchase obligations	$ 39,941,000
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	$ 944,824,000
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	43,299,000
Capital Leases, Future Minimum Payments Due	$ 100,935,000