Construction Contracts (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Capitalized contract cost, amortization	$ 100	$ 100
Construction receivables retentions	3,400		$ 8,500
Retention payable	3,622	$ 2,235	3,037	$ 3,591
Construction
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Retention payable	18,000		21,600
Portion Attributable To Pending Contracts
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred pre-contract costs	$ 1,500		$ 1,400