Business Segments (Total Assets For Reportable Segments) (Details) - USD ($) $ in Thousands		Jun. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Assets		$ 4,763,603	$ 4,485,777
Civil [Member]
Segment Reporting Information [Line Items]
Assets		3,084,528	2,791,402
Building [Member]
Segment Reporting Information [Line Items]
Assets		1,083,421	995,298
Specialty Contractors [Member]
Segment Reporting Information [Line Items]
Assets		664,161	635,180
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Assets	[1]	$ (68,507)	$ 63,897

[1] Consists principally of cash, equipment, tax-related assets and insurance-related assets, offset by the elimination of assets related to intersegment revenue.