Business Segments (Schedule of Assets by Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Reportable segment information
Total Assets	$ 4,195,585	$ 4,036,677
Civil [Member]
Reportable segment information
Total Assets	2,044,060	1,964,038
Building [Member]
Reportable segment information
Total Assets	882,465	795,851
Specialty Contractors [Member]
Reportable segment information
Total Assets	803,073	860,285
Corporate [Member]
Reportable segment information
Total Assets	$ 465,987	$ 416,503