Business Segments (Schedule of Assets by Segment) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Reportable segment information
Total Assets	$ 3,943,636	$ 3,773,315
Building [Member]
Reportable segment information
Total Assets	671,060	680,933
Civil [Member]
Reportable segment information
Total Assets	1,934,040	1,814,170
Specialty Contractors [Member]
Reportable segment information
Total Assets	863,831	775,162
Reportable Segments [Member]
Reportable segment information
Total Assets	3,468,931	3,270,265
Corporate [Member]
Reportable segment information
Total Assets	$ 474,705	$ 503,050