Business Segments (Schedule of Assets by Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Reportable segment information
Total Assets	$ 4,413,496	$ 4,387,752
Civil [Member]
Reportable segment information
Total Assets	2,545,572	2,574,326
Building [Member]
Reportable segment information
Total Assets	961,287	913,746
Specialty Contractors [Member]
Reportable segment information
Total Assets	607,008	745,313
Corporate and Other [Member]
Reportable segment information
Total Assets	$ 299,629	$ 154,367