Construction Contracts - Summary of Backlog (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Remaining Performance Obligation [Roll Forward]
Beginning backlog	$ 37,921	$ 116,657	$ 49,167	$ 217,718
New contracts/change orders	7,138	1,251	39,514	20,211
Work performed	(19,879)	(41,165)	(63,501)	(161,186)
Ending backlog	$ 25,180	$ 76,743	$ 25,180	$ 76,743
Minimum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected completion of contracts	12 months		12 months
Maximum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected completion of contracts	18 months		18 months