Commitments and Contingencies (Details Textuals) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies (Textuals) [Abstract]
Number of outstanding letters of credit	9
Outstanding letters of credit	$ 96,096,000
Additional financing to complete construction	525,588,000
Total contingent purchase obligations	24,088,000
Operating lease obligations relating to certain ground leases	990,027,000
Aggregate future minimum rentals to be received	26,445,000
Gross assets under capital lease recorded in real property	167,324,000
Outstanding construction financings for leased properties	258,968,000	$ 186,327,000
Accumulated Depreciation assets under capital lease recorded in real property	$ 20,555,000
Minimum part of economic life of leased asset to be classified as capital lease	75.00%
Minimum net present value of future minimum lease payments to be classified as capital lease	90.00%
Letter of credit expiration date maximum	Dec. 31, 2018
Letter of credit expiration date minimum	Jan. 01, 2016