Business Segments (Reportable Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Business Segments [Line items]
Revenue	$ 1,199,505	$ 1,332,978	$ 3,564,140	$ 3,726,477
INCOME FROM CONSTRUCTION OPERATIONS	49,072	60,919	120,134	149,870
Other income, net	967	2,048	42,373	5,214
Capital expenditures	1,529	1,592	9,712	10,273
Depreciation and amortization	9,705	17,339	40,463	47,295
External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	1,269,044	1,398,508	3,791,896	3,905,765
Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(69,539)	(65,530)	(227,756)	(179,288)
Reportable Segments [Member]
Business Segments [Line items]
Revenue	1,199,505	1,332,978	3,564,140	3,726,477
INCOME FROM CONSTRUCTION OPERATIONS	66,777	74,687	168,541	193,907
Capital expenditures	1,365	1,475	9,223	9,678
Depreciation and amortization	6,881	14,453	31,851	38,658
Reportable Segments [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	1,269,044	1,398,508	3,791,896	3,905,765
Reportable Segments [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(69,539)	(65,530)	(227,756)	(179,288)
Civil [Member]
Business Segments [Line items]
Revenue	395,820	458,823	1,172,977	1,260,388
INCOME FROM CONSTRUCTION OPERATIONS	38,144	50,307	128,176	129,028
Capital expenditures	1,248	1,342	8,665	8,499
Depreciation and amortization	5,213	12,669	26,767	33,200
Civil [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	458,487	506,100	1,363,850	1,378,531
Civil [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(62,667)	(47,277)	(190,873)	(118,143)
Building [Member]
Business Segments [Line items]
Revenue	493,548	542,542	1,483,473	1,533,801
INCOME FROM CONSTRUCTION OPERATIONS	14,058	13,296	25,035	38,969
Capital expenditures	36	79	184	381
Depreciation and amortization	502	541	1,533	1,647
Building [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	500,420	560,795	1,520,356	1,594,946
Building [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(6,872)	(18,253)	(36,883)	(61,145)
Specialty Contractors [Member]
Business Segments [Line items]
Revenue	310,137	331,613	907,690	932,288
INCOME FROM CONSTRUCTION OPERATIONS	14,575	11,084	15,330	25,910
Capital expenditures	81	54	374	798
Depreciation and amortization	1,166	1,243	3,551	3,811
Specialty Contractors [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	310,137	331,613	907,690	932,288
Corporate [Member]
Business Segments [Line items]
INCOME FROM CONSTRUCTION OPERATIONS	(17,705)	(13,768)	(48,407)	(44,037)
Capital expenditures	164	117	489	595
Depreciation and amortization	$ 2,824	$ 2,886	$ 8,612	$ 8,637