Business Segments (Schedule of Assets by Segment) (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Reportable segment information
Total Assets		$ 4,556,270	$ 4,387,752
Civil [Member]
Reportable segment information
Total Assets		2,606,842	2,574,326
Building [Member]
Reportable segment information
Total Assets		936,099	913,746
Specialty Contractors [Member]
Reportable segment information
Total Assets		744,509	745,313
Corporate and Other [Member]
Reportable segment information
Total Assets	[1]	$ 268,820	$ 154,367

[1] Consists principally of cash, equipment, tax-related assets and insurance-related assets, offset by the elimination of assets related to intersegment revenue.