Business Segments (Reportable Segments) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020		Jun. 30, 2019
Business Segments
Revenues		$ 1,276,427		$ 1,125,275		$ 2,527,156		$ 2,083,762
Income (loss) from construction operations		57,696		(341,717)		104,923		(318,804)
Capital expenditures		19,693		24,934		31,386		39,346
Depreciation and amortization	[1]	25,965		14,597		48,776		28,314
Net income (loss)		$ 30,859		$ (315,439)		$ 56,997		$ (310,717)
DILUTED EARNINGS (LOSS) PER COMMON SHARE		$ 0.37		$ (6.38)		$ 0.71		$ (6.40)
Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		$ (93,072)		$ (72,700)		$ (209,964)		$ (125,605)
External and Intersegment Customers [Member]
Business Segments
Revenues		1,369,499		1,197,975		2,737,120		2,209,367
Reporting Segments [Member]
Business Segments
Revenues		1,276,427		1,125,275		2,527,156		2,083,762
Income (loss) from construction operations		71,799	[2]	(328,077)	[3]	129,715	[4]	(290,687)	[5]
Capital expenditures		19,392		24,699		31,069		38,889
Depreciation and amortization	[1]	23,198		11,843		43,234		22,780
Reporting Segments [Member] | Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		(93,072)		(72,700)		(209,964)		(125,605)
Reporting Segments [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues		1,369,499		1,197,975		2,737,120		2,209,367
Civil [Member]
Business Segments
Revenues		568,976		473,658		1,055,605		807,152
Income (loss) from construction operations		65,398		(164,472)		111,519		(122,727)
Capital expenditures		18,951		24,439		30,143		38,451
Depreciation and amortization	[1]	21,775		10,285		40,391		19,655
Civil [Member] | Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		(75,709)		(67,459)		(169,166)		(117,587)
Civil [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues		644,685		541,117		1,224,771		924,739
Building [Member]
Business Segments
Revenues		473,021		428,318		954,785		861,784
Income (loss) from construction operations		17,789		(3,810)		21,305		(677)
Capital expenditures		186		150		198		205
Depreciation and amortization	[1]	428		497		855		1,000
Building [Member] | Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		(17,296)		(5,241)		(40,615)		(8,018)
Building [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues		490,317		433,559		995,400		869,802
Specialty Contractors [Member]
Business Segments
Revenues		234,430		223,299		516,766		414,826
Income (loss) from construction operations		(11,388)		(159,795)		(3,109)		(167,283)
Capital expenditures		255		110		728		233
Depreciation and amortization	[1]	995		1,061		1,988		2,125
Specialty Contractors [Member] | Elimination Of Intersegment Revenue [Member]
Business Segments
Revenues		(67)				(183)
Specialty Contractors [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues		234,497		223,299		516,949		414,826
Corporate [Member]
Business Segments
Income (loss) from construction operations	[6]	(14,103)		(13,640)		(24,792)		(28,117)
Capital expenditures		301		235		317		457
Depreciation and amortization	[1]	2,767		2,754		5,542		5,534
Unfavorable Adjustments [Member]
Business Segments
Income (loss) from construction operations		13,200		379,900		13,200		379,900
Net income (loss)		$ 9,500		$ 329,500		$ 9,500		$ 329,500
DILUTED EARNINGS (LOSS) PER COMMON SHARE		$ 0.19		$ 6.56		$ 0.19		$ 6.57

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

[2] During the three months ended June 30, 2020, income (loss) from construction operations was impacted by $13.2 million (an unfavorable after-tax impact of $9.5 million, or $0.19 per diluted share) due to an adverse arbitration ruling pertaining to an electrical project in New York in the Specialty Contractors segment.

[3] During the three months ended June 30, 2019, the Company recorded a non-cash goodwill impairment charge of $379.9 million in income (loss) from construction operations (an unfavorable after-tax impact of $329.5 million, or $6.56 per diluted share) resulting from an interim impairment test the Company performed as of June 1, 2019.

[4] During the six months ended June 30, 2020, income (loss) from construction operations was impacted by $13.2 million (an unfavorable after-tax impact of $9.5 million, or $0.19 per diluted share) due to an adverse arbitration ruling pertaining to an electrical project in New York in the Specialty Contractors segment.

[5] During the six months ended June 30, 2019, the Company recorded a non-cash goodwill impairment charge of $379.9 million in income (loss) from construction operations (an unfavorable after-tax impact of $329.5 million, or $6.57 per diluted share) resulting from an interim impairment test the Company performed as of June 1, 2019.

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