Construction Contracts - Summary of Backlog (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue, Remaining Performance Obligation [Roll Forward]
Beginning backlog	$ 165,863	$ 49,167
New contracts/change orders	12,019	4,569
Work performed	(17,011)	(23,003)
Ending backlog	$ 160,871	$ 30,733
Minimum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected completion of contracts	12 months
Maximum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected completion of contracts	18 months