Business Segments (Reportable Segments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Business Segments [Line items]
Revenue	$ 1,117,361	$ 1,085,369
Income from construction operations	37,017	40,122
Other income, net	417	682
Capital expenditures	5,672	4,812
Depreciation and amortization	20,996	12,809
External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	1,169,055	1,137,268
Revenue From External Customer [Member]
Business Segments [Line items]
Revenue	1,117,361	1,085,369
Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(51,694)	(51,899)
Operating segment [Member]
Business Segments [Line items]
Revenue	1,169,055	1,137,268
Income from construction operations	51,892	55,528
Capital expenditures	5,618	4,458
Depreciation and amortization	18,028	9,945
Operating segment [Member] | Revenue From External Customer [Member]
Business Segments [Line items]
Revenue	1,117,361	1,085,369
Operating segment [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(51,694)	(51,899)
Civil [Member]
Business Segments [Line items]
Revenue	338,108	367,501
Income from construction operations	31,888	33,665
Capital expenditures	5,567	3,612
Depreciation and amortization	16,318	8,083
Civil [Member] | Revenue From External Customer [Member]
Business Segments [Line items]
Revenue	304,575	335,858
Civil [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(33,533)	(31,643)
Building [Member]
Business Segments [Line items]
Revenue	515,251	487,994
Income from construction operations	5,242	12,450
Capital expenditures	45	221
Depreciation and amortization	518	557
Building [Member] | Revenue From External Customer [Member]
Business Segments [Line items]
Revenue	497,090	467,738
Building [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(18,161)	(20,256)
Specialty Contractors [Member]
Business Segments [Line items]
Revenue	315,696	281,773
Income from construction operations	14,762	9,413
Capital expenditures	6	625
Depreciation and amortization	1,192	1,305
Specialty Contractors [Member] | Revenue From External Customer [Member]
Business Segments [Line items]
Revenue	315,696	281,773
Corporate [Member]
Business Segments [Line items]
Income from construction operations	(14,875)	(15,406)
Capital expenditures	54	354
Depreciation and amortization	$ 2,968	$ 2,864