Revenue Recognition on Construction Contract and Other Service Revenues (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Change in Accounts Receivable
Beginning balance	$ 23,656		$ 23,656		$ 31,802
Ending balance	23,656		23,656		31,802
Construction Contract Revenue
Change in Accounts Receivable
Beginning balance	4,805	$ 11,946	4,805	$ 11,946	4,577	$ 4,131
Ending balance	4,805	11,946	4,805	11,946	4,577	4,131
Change in Contract with Customer, Asset
Beginning balance	4,158	3,620	4,158	3,620	4,884	10,350
Ending balance	4,158	3,620	4,158	3,620	4,884	10,350
Change in Contract with Customer, Liability
Beginning balance	515	40,209	515	40,209	27,402	32,650
Ending balance	515	40,209	515	40,209	$ 27,402	$ 32,650
Revenue recognized included in beginning balance	$ 7,999	$ 16,762	$ 27,296	$ 20,961