Construction Contracts (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Contractors [Abstract]
Construction receivables retentions	$ 8,600	$ 9,900
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Retention payable	1,767	3,591
Construction
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Retention payable	20,100	17,400
Portion Attributable To Pending Contracts
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred pre-contract costs	$ 700	$ 600