Business Segments (Reportable Segments) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Business Segments
Revenues		$ 1,250,729	$ 958,487
Income (loss) from construction operations		47,227	22,913
Capital expenditures		11,693	14,412
Depreciation and amortization	[1]	22,811	13,717
Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		(116,892)	(52,905)
External and Intersegment Customers [Member]
Business Segments
Revenues		1,367,621	1,011,392
Reporting Segments [Member]
Business Segments
Revenues		1,250,729	958,487
Income (loss) from construction operations		57,916	37,390
Capital expenditures		11,677	14,190
Depreciation and amortization	[1]	20,036	10,937
Reporting Segments [Member] | Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		(116,892)	(52,905)
Reporting Segments [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues		1,367,621	1,011,392
Civil [Member]
Business Segments
Revenues		486,629	333,494
Income (loss) from construction operations		46,121	41,745
Capital expenditures		11,192	14,012
Depreciation and amortization	[1]	18,616	9,370
Civil [Member] | Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		(93,458)	(50,128)
Civil [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues		580,087	383,622
Building [Member]
Business Segments
Revenues		481,764	433,466
Income (loss) from construction operations		3,516	3,133
Capital expenditures		12	55
Depreciation and amortization	[1]	427	503
Building [Member] | Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		(23,318)	(2,777)
Building [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues		505,082	436,243
Specialty Contractors [Member]
Business Segments
Revenues		282,336	191,527
Income (loss) from construction operations		8,279	(7,488)
Capital expenditures		473	123
Depreciation and amortization	[1]	993	1,064
Specialty Contractors [Member] | Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		(116)
Specialty Contractors [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues		282,452	191,527
Corporate [Member]
Business Segments
Income (loss) from construction operations	[2]	(10,689)	(14,477)
Capital expenditures		16	222
Depreciation and amortization	[1]	$ 2,775	$ 2,780

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

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