Commitments and Contingencies (Details Textual)	9 Months Ended
	Sep. 30, 2018 USD ($) obligation	Dec. 31, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Number of outstanding credit obligations | obligation	13
Letter of credit obligation	$ 51,684,000
Outstanding construction financings for leased properties	135,343,000	$ 237,746,000
Additional financing to complete construction	332,834,000
Total contingent purchase obligations	$ 10,245,000
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	$ 1,107,336,000
Capital leases, future minimum payments due	85,308,000
Operating leases, future minimum payments due, future minimum sublease rentals	$ 73,771,000