Commitments and Contingencies (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012 Number	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Commitments and Contingencies (Textual) [Abstract]
Number of outstanding letters of credit	6
Letter of credit obligation	$ 5,925		$ 5,925
Outstanding construction financings for leased properties	170,785		170,785		189,502
Additional financing to complete construction	201,261		201,261
Total contingent purchase obligations	62,347		62,347
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%		90.00%
Operating lease obligations relating to certain ground leases		531,618		531,618
Rental expense related to company office space	312	615	601	1,130
Aggregated future minimum rentals to be received	$ 41,912		$ 41,912