Business Segments (Reportable Segments) (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenue	$ 1,442,091,000		$ 1,189,345,000	$ 3,969,247,000	$ 3,273,107,000
Income (loss) from construction operations	83,021,000		47,943,000	187,944,000	(270,861,000)
Capital expenditures	12,010,000		23,331,000	43,396,000	62,677,000
Depreciation and amortization	30,858,000		16,227,000	79,634,000	44,541,000
Goodwill impairment	0	$ 0	0	0	379,863,000
Goodwill impairment, after tax					$ 329,500,000
Goodwill impairment, after tax, per diluted share (in dollars per share)					$ 6.56
Operating Segments
Segment Reporting Information [Line Items]
Revenue	1,598,238,000		1,262,578,000	4,335,358,000	$ 3,471,945,000
Income (loss) from construction operations	95,752,000		65,522,000	225,467,000	(225,165,000)
Capital expenditures	11,658,000		22,966,000	42,727,000	61,855,000
Depreciation and amortization	28,080,000		13,466,000	71,314,000	36,246,000
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue	(156,147,000)		(73,233,000)	(366,111,000)	(198,838,000)
Corporate
Segment Reporting Information [Line Items]
Income (loss) from construction operations	(12,731,000)		(17,579,000)	(37,523,000)	(45,696,000)
Capital expenditures	352,000		365,000	669,000	822,000
Depreciation and amortization	2,778,000		2,761,000	8,320,000	8,295,000
Civil
Segment Reporting Information [Line Items]
Revenue	611,996,000		524,546,000	1,667,601,000	1,331,698,000
Civil | Operating Segments
Segment Reporting Information [Line Items]
Revenue	723,324,000		591,884,000	1,948,095,000	1,516,623,000
Income (loss) from construction operations	70,237,000		50,695,000	181,756,000	(72,032,000)
Capital expenditures	10,996,000		22,497,000	41,139,000	60,948,000
Depreciation and amortization	26,659,000		11,953,000	67,050,000	31,608,000
Civil | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue	(111,328,000)		(67,338,000)	(280,494,000)	(184,925,000)
Building
Segment Reporting Information [Line Items]
Revenue	508,140,000		415,346,000	1,462,925,000	1,277,130,000
Building | Operating Segments
Segment Reporting Information [Line Items]
Revenue	552,823,000		421,241,000	1,548,223,000	1,291,043,000
Income (loss) from construction operations	15,815,000		7,580,000	37,120,000	6,903,000
Capital expenditures	438,000		144,000	636,000	349,000
Depreciation and amortization	419,000		495,000	1,274,000	1,495,000
Building | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue	(44,683,000)		(5,895,000)	(85,298,000)	(13,913,000)
Specialty Contractors
Segment Reporting Information [Line Items]
Revenue	321,955,000		249,453,000	838,721,000	664,279,000
Specialty Contractors | Favorable Arbitration Decision
Segment Reporting Information [Line Items]
Adverse arbitration, loss in period	19,600,000			19,600,000
Adverse arbitration, loss in period, after tax	$ 14,100,000			$ 14,100,000
Adverse arbitration, loss in period, after tax, per diluted share (in dollars per share)	$ 0.28			$ 0.28
Specialty Contractors | Unfavorable Legal Ruling Pertaining To Mechanical Project In California
Segment Reporting Information [Line Items]
Adverse arbitration, loss in period	$ 15,200,000			$ 15,200,000
Adverse arbitration, loss in period, after tax	$ 10,900,000			$ 10,900,000
Adverse arbitration, loss in period, after tax, per diluted share (in dollars per share)	$ 0.21			$ 0.21
Specialty Contractors | Adverse Arbitration Ruling Pertaining To Electrical Project In New York
Segment Reporting Information [Line Items]
Adverse arbitration, loss in period				$ 13,200,000
Adverse arbitration, loss in period, after tax				$ 9,500,000
Adverse arbitration, loss in period, after tax, per diluted share (in dollars per share)				$ 0.19
Specialty Contractors | Operating Segments
Segment Reporting Information [Line Items]
Revenue	$ 322,091,000		249,453,000	$ 839,040,000	664,279,000
Income (loss) from construction operations	9,700,000		7,247,000	6,591,000	(160,036,000)
Capital expenditures	224,000		325,000	952,000	558,000
Depreciation and amortization	1,002,000		1,018,000	2,990,000	3,143,000
Specialty Contractors | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue	$ (136,000)		$ 0	$ (319,000)	$ 0