Construction Contracts - Summary of Backlog (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue, Remaining Performance Obligation [Roll Forward]
Beginning backlog	$ 160,871	$ 30,733	$ 165,863	$ 49,167
New contracts/change orders	39,177	27,807	51,196	32,376
Work performed	(21,416)	(20,619)	(38,427)	(43,622)
Ending backlog	$ 178,632	$ 37,921	$ 178,632	$ 37,921
Minimum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-07-01
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]: 2019-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected completion of contracts	18 months		18 months