Business Segments (Reportable Segments) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Business Segments
Revenues		$ 1,183,284	$ 1,123,137	$ 1,120,085	$ 1,028,156	$ 1,193,068	$ 1,199,505	$ 1,247,274	$ 1,117,361	$ 4,454,662		$ 4,757,208	$ 4,973,076
Income from construction operations		$ 90,680	$ 47,306	$ 54,815	$ (925)	$ 59,343	$ 49,072	$ 34,045	$ 37,017	191,876		179,477	201,920
Capital Expenditures										77,069		30,280	15,743
Depreciation and amortization	[1]									47,267		51,930	67,302
Intersubsegment Eliminations [Member]
Business Segments
Revenues										(229,342)		(295,521)	(238,800)
External and Intersegment Customers [Member]
Business Segments
Revenues										4,684,004		5,052,729	5,211,876
Reportable Segments [Member]
Business Segments
Revenues										4,454,662		4,757,208	4,973,076
Income from construction operations										255,625	[2]	245,344	262,140	[3]
Capital Expenditures										76,298		28,682	15,062
Depreciation and amortization	[1]									35,999		40,487	55,782
Reportable Segments [Member] | Intersubsegment Eliminations [Member]
Business Segments
Revenues										(229,342)		(295,521)	(238,800)
Reportable Segments [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues										4,684,004		5,052,729	5,211,876
Civil
Business Segments
Revenues										1,586,093		1,602,175	1,668,963
Income from construction operations										168,256	[2]	192,207	172,668	[3]
Capital Expenditures										73,866		27,694	13,541
Depreciation and amortization	[1]									29,685		33,767	48,561
Civil | Intersubsegment Eliminations [Member]
Business Segments
Revenues										(224,139)		(253,989)	(161,894)
Civil | External and Intersegment Customers [Member]
Business Segments
Revenues										1,810,232		1,856,164	1,830,857
Building
Business Segments
Revenues										1,861,699		1,941,325	2,069,841
Income from construction operations										43,939	[2]	34,199	51,564	[3]
Capital Expenditures										1,655		267	516
Depreciation and amortization	[1]									1,956		2,021	2,186
Building | Intersubsegment Eliminations [Member]
Business Segments
Revenues										(5,203)		(41,532)	(76,906)
Building | External and Intersegment Customers [Member]
Business Segments
Revenues										1,866,902		1,982,857	2,146,747
Specialty Contractors
Business Segments
Revenues										1,006,870		1,213,708	1,234,272
Income from construction operations										43,430	[2]	18,938	37,908	[3]
Capital Expenditures										777		721	1,005
Depreciation and amortization	[1]									4,358		4,699	5,035
Specialty Contractors | External and Intersegment Customers [Member]
Business Segments
Revenues										1,006,870		1,213,708	1,234,272
Corporate [Member]
Business Segments
Income from construction operations	[4]									(63,749)	[2]	(65,867)	(60,220)	[3]
Capital Expenditures										771		1,598	681
Depreciation and amortization	[1]									$ 11,268		$ 11,443	$ 11,520

[1] Depreciation and amortization is included in income from construction operations.

[2] During the year ended December 31, 2018, the Company recorded a charge of $17.8 million in income from construction operations (an after-tax impact of $12.8 million, or $0.25 per diluted share), which was primarily non-cash, as a result of the unexpected outcome of an arbitration decision related to a subcontract back charge dispute on a Civil segment project in New York that was completed in 2013.

[3] During the year ended December 31, 2016 the Company recorded net favorable adjustments totaling $3.0 million in income from construction operations (an after-tax impact of $1.8 million, or $0.04 per diluted share) for various Five Star Electric projects in New York in the Specialty Contractors segment. The net impact included material adjustments related to two electrical subcontract projects: a favorable adjustment of $14.0 million for a completed project (an after-tax impact of $8.2 million, or $0.17 per diluted share) and an unfavorable adjustment of $13.8 million for a project that was nearly complete (an after-tax impact of $8.1 million, or $0.16 per diluted share).

[4] Consists primarily of corporate general and administrative expenses.