Business Segments (Schedule of Assets by Segment) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Reportable segment information
Total Assets	$ 3,970,255	$ 3,773,315
Building [Member]
Reportable segment information
Total Assets	794,274	680,933
Civil [Member]
Reportable segment information
Total Assets	1,973,925	1,814,170
Specialty Contractors [Member]
Reportable segment information
Total Assets	863,750	775,162
Reportable Segments [Member]
Reportable segment information
Total Assets	3,631,949	3,270,265
Corporate [Member]
Reportable segment information
Total Assets	$ 338,306	$ 503,050