Business Segments (Reportable Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Business Segments [Line items]
Revenue	$ 1,332,978	$ 1,340,739	$ 3,726,477	$ 3,719,642
Income from construction operations	60,919	38,974	149,870	89,939
Other income, net	2,048	6,195	5,214	6,098
Interest expense	(15,041)	(11,214)	(44,655)	(33,885)
INCOME BEFORE INCOME TAXES	47,926	33,955	110,429	62,152
Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(65,530)	(95,202)	(179,288)	(190,660)
Operating segment [Member]
Business Segments [Line items]
Revenue	1,398,508	1,435,941	3,905,765	3,910,302
Reportable Segments [Member]
Business Segments [Line items]
Revenue	1,332,978	1,340,739	3,726,477	3,719,642
Income from construction operations	74,687	54,687	193,907	141,007
Reportable Segments [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(65,530)	(95,202)	(179,288)	(190,660)
Reportable Segments [Member] | Operating segment [Member]
Business Segments [Line items]
Revenue	1,398,508	1,435,941	3,905,765	3,910,302
Civil [Member]
Business Segments [Line items]
Revenue	458,823	540,250	1,260,388	1,449,104
Income from construction operations	50,307	43,183	129,028	120,106
Civil [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(47,277)	(64,067)	(118,143)	(121,449)
Civil [Member] | Operating segment [Member]
Business Segments [Line items]
Revenue	506,100	604,317	1,378,531	1,570,553
Building [Member]
Business Segments [Line items]
Revenue	542,542	475,124	1,533,801	1,325,357
Income from construction operations	13,296	6,763	38,969	(8,107)
Building [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(18,253)	(31,135)	(61,145)	(69,211)
Building [Member] | Operating segment [Member]
Business Segments [Line items]
Revenue	560,795	506,259	1,594,946	1,394,568
Specialty Contractors [Member]
Business Segments [Line items]
Revenue	331,613	325,365	932,288	945,181
Income from construction operations	11,084	4,741	25,910	29,008
Specialty Contractors [Member] | Operating segment [Member]
Business Segments [Line items]
Revenue	331,613	325,365	932,288	945,181
Corporate [Member]
Business Segments [Line items]
Income from construction operations	$ (13,768)	$ (15,713)	$ (44,037)	$ (51,068)