Business Segments (Reportable Segments) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenue	$ 1,219,243	$ 1,276,427	$ 2,426,838	$ 2,527,156
Income (loss) from construction operations	68,753	57,696	118,457	104,923
Capital expenditures	9,025	19,693	18,860	31,386
Depreciation and amortization	35,261	25,965	62,135	48,776
Operating Segments
Segment Reporting Information [Line Items]
Revenue	1,340,226	1,369,499	2,705,488	2,737,120
Income (loss) from construction operations	82,545	71,799	145,190	129,715
Capital expenditures	8,686	19,392	18,468	31,069
Depreciation and amortization	32,494	23,198	56,598	43,234
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue	(120,983)	(93,072)	(278,650)	(209,964)
Corporate
Segment Reporting Information [Line Items]
Income (loss) from construction operations	(13,792)	(14,103)	(26,733)	(24,792)
Capital expenditures	339	301	392	317
Depreciation and amortization	2,767	2,767	5,537	5,542
Civil
Segment Reporting Information [Line Items]
Revenue	555,352	568,976	1,030,927	1,055,605
Civil | Operating Segments
Segment Reporting Information [Line Items]
Revenue	643,055	644,685	1,226,199	1,224,771
Income (loss) from construction operations	75,073	65,398	125,178	111,519
Capital expenditures	8,616	18,951	18,180	30,143
Depreciation and amortization	31,178	21,775	53,891	40,391
Civil | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue	(87,703)	(75,709)	(195,272)	(169,166)
Building
Segment Reporting Information [Line Items]
Revenue	382,660	473,021	789,893	954,785
Building | Operating Segments
Segment Reporting Information [Line Items]
Revenue	415,801	490,317	872,971	995,400
Income (loss) from construction operations	(2,488)	17,789	8,728	21,305
Capital expenditures	51	186	124	198
Depreciation and amortization	424	428	856	855
Building | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue	(33,141)	(17,296)	(83,078)	(40,615)
Specialty Contractors
Segment Reporting Information [Line Items]
Revenue	281,231	234,430	606,018	516,766
Specialty Contractors | Adverse Arbitration Ruling Pertaining To Electrical Project In New York
Segment Reporting Information [Line Items]
Adverse arbitration, loss in period		13,200		13,200
Adverse arbitration, loss in period, after tax		$ 9,500		$ 9,500
Adverse arbitration, loss in period, after tax, diluted (in dollars per share)		$ 0.19		$ 0.19
Specialty Contractors | Favorable Legal Ruling Pertaining To Electrical Project In New York
Segment Reporting Information [Line Items]
Favorable arbitration, reduction in cost of operations	20,100		20,100
Favorable arbitration, reduction in cost of operations, after tax	$ 14,600		$ 14,600
Favorable arbitration, reduction in cost of operations, after tax, diluted (in dollars per share)	$ 0.28		$ 0.28
Specialty Contractors | Operating Segments
Segment Reporting Information [Line Items]
Revenue	$ 281,370	$ 234,497	$ 606,318	$ 516,949
Income (loss) from construction operations	9,960	(11,388)	11,284	(3,109)
Capital expenditures	19	255	164	728
Depreciation and amortization	892	995	1,851	1,988
Specialty Contractors | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue	$ (139)	$ (67)	$ (300)	$ (183)