Business Segments (Reportable Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Business Segments [Line items]
Revenue	$ 1,308,130	$ 1,312,438	$ 2,393,499	$ 2,378,903
Income from construction operations	48,829	30,881	88,951	50,965
Other income (expense), net	2,485	379	3,166	(97)
Interest expense	(15,534)	(11,268)	(29,614)	(22,671)
INCOME BEFORE INCOME TAXES	35,780	19,992	62,503	28,197
Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(61,859)	(59,967)	(113,758)	(95,458)
Operating segment [Member]
Business Segments [Line items]
Revenue	1,369,989	1,372,405	2,507,257	2,474,361
Reportable Segments [Member]
Business Segments [Line items]
Revenue	1,308,130	1,312,438	2,393,499	2,378,903
Income from construction operations	63,692	47,480	119,220	86,320
Reportable Segments [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(61,859)	(59,967)	(113,758)	(95,458)
Reportable Segments [Member] | Operating segment [Member]
Business Segments [Line items]
Revenue	1,369,989	1,372,405	2,507,257	2,474,361
Civil [Member]
Business Segments [Line items]
Revenue	465,707	534,180	801,565	908,854
Income from construction operations	45,056	46,329	78,721	76,923
Civil [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(39,223)	(39,180)	(70,866)	(57,382)
Civil [Member] | Operating segment [Member]
Business Segments [Line items]
Revenue	504,930	573,360	872,431	966,236
Building [Member]
Business Segments [Line items]
Revenue	523,521	451,404	991,259	850,233
Income from construction operations	13,223	(12,592)	25,673	(14,870)
Building [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(22,636)	(20,843)	(42,892)	(38,076)
Building [Member] | Operating segment [Member]
Business Segments [Line items]
Revenue	546,157	472,247	1,034,151	888,309
Specialty Contractors [Member]
Business Segments [Line items]
Revenue	318,902	326,854	600,675	619,816
Income from construction operations	5,413	13,743	14,826	24,267
Specialty Contractors [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue		56
Specialty Contractors [Member] | Operating segment [Member]
Business Segments [Line items]
Revenue	318,902	326,798	600,675	619,816
Corporate [Member]
Business Segments [Line items]
Income from construction operations	$ (14,863)	$ (16,599)	$ (30,269)	$ (35,355)