Business Segments (Reportable Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Business Segments [Line items]
Revenue	$ 1,247,274	$ 1,308,130	$ 2,364,635	$ 2,393,499
INCOME FROM CONSTRUCTION OPERATIONS	34,045	48,829	71,062	88,951
Other income, net	40,990	2,485	41,406	3,166
Capital expenditures	2,511	3,869	8,183	8,681
Depreciation and amortization	9,762	17,146	30,758	29,956
External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	1,329,178	1,369,989	2,522,852	2,507,257
Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(81,904)	(61,859)	(158,217)	(113,758)
Reportable Segments [Member]
Business Segments [Line items]
Revenue	1,247,274	1,308,130	2,364,635	2,393,499
INCOME FROM CONSTRUCTION OPERATIONS	49,873	63,692	101,764	119,220
Capital expenditures	2,240	3,745	7,858	8,203
Depreciation and amortization	6,942	14,259	24,970	24,205
Reportable Segments [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	1,329,178	1,369,989	2,522,852	2,507,257
Reportable Segments [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(81,904)	(61,859)	(158,217)	(113,758)
Civil [Member]
Business Segments [Line items]
Revenue	472,582	465,707	777,157	801,565
INCOME FROM CONSTRUCTION OPERATIONS	58,144	45,056	90,032	78,721
Capital expenditures	1,850	3,545	7,417	7,157
Depreciation and amortization	5,236	12,447	21,554	20,531
Civil [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	538,552	504,930	905,363	872,431
Civil [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(65,970)	(39,223)	(128,206)	(70,866)
Building [Member]
Business Segments [Line items]
Revenue	492,835	523,521	989,925	991,259
INCOME FROM CONSTRUCTION OPERATIONS	5,736	13,223	10,977	25,673
Capital expenditures	104	81	148	302
Depreciation and amortization	513	549	1,031	1,106
Building [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	508,769	546,157	1,019,936	1,034,151
Building [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(15,934)	(22,636)	(30,011)	(42,892)
Specialty Contractors [Member]
Business Segments [Line items]
Revenue	281,857	318,902	597,553	600,675
INCOME FROM CONSTRUCTION OPERATIONS	(14,007)	5,413	755	14,826
Capital expenditures	286	119	293	744
Depreciation and amortization	1,193	1,263	2,385	2,568
Specialty Contractors [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	281,857	318,902	597,553	600,675
Corporate [Member]
Business Segments [Line items]
INCOME FROM CONSTRUCTION OPERATIONS	(15,828)	(14,863)	(30,702)	(30,269)
Capital expenditures	271	124	325	478
Depreciation and amortization	$ 2,820	$ 2,887	$ 5,788	$ 5,751