Business Segments (Schedule of Assets by Segment) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Reportable segment information
Total Assets	$ 4,131,482	$ 4,036,677
Civil [Member]
Reportable segment information
Total Assets	1,947,787	1,964,038
Building [Member]
Reportable segment information
Total Assets	902,669	795,851
Specialty Contractors [Member]
Reportable segment information
Total Assets	843,379	860,285
Corporate [Member]
Reportable segment information
Total Assets	$ 437,647	$ 416,503