Construction Contracts (Summary of Backlog) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Remaining Performance Obligation [Roll Forward]
Beginning backlog	$ 49,167	$ 217,718	$ 83,433
New contracts/change orders	192,852	25,224	293,115
Work performed	(76,156)	(193,775)	(158,830)
Ending backlog	$ 165,863	$ 49,167	$ 217,718
Minimum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
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]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected completion of contracts	18 months