Commitments and Contingencies (Details Textual) (USD $)	3 Months Ended
	Mar. 31, 2015 Number	Dec. 31, 2014
Commitments and Contingencies (Textual) [Abstract]
Number of outstanding letters of credit	7
Letter of credit obligation	$ 10,769,000
Outstanding construction financings for leased properties	211,941,000	186,327,000
Additional financing to complete construction	355,231,000
Total contingent purchase obligations	59,856,000
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	948,535,000
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	28,834,000
Capital Leases, Future Minimum Payments Due	$ 102,117,000