Construction Contracts (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Contractors [Abstract]
Deferred pre-contract costs	$ 500	$ 600
Construction receivables retentions	8,900	9,900
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Retention payable	1,711	3,591
Construction
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Retention payable	$ 17,400	$ 17,400