Business Segments (Reportable Segments) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Segments [Line items]
Revenue	$ 1,125,275	$ 1,120,085	$ 2,083,762	$ 2,148,241
Income (loss) from construction operations	(341,717)	54,815	(318,804)	53,890
Capital expenditures	24,934	28,333	39,346	48,303
Depreciation and amortization	14,597	10,977	28,314	21,164
External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	1,197,975	1,180,222	2,209,367	2,271,040
Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(72,700)	(60,137)	(125,605)	(122,799)
Reportable Segments [Member]
Business Segments [Line items]
Revenue	1,125,275	1,120,085	2,083,762	2,148,241
Income (loss) from construction operations	(328,077)	69,429	(290,687)	85,928
Capital expenditures	24,699	28,159	38,889	48,052
Depreciation and amortization	11,843	8,164	22,780	15,513
Reportable Segments [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	1,197,975	1,180,222	2,209,367	2,271,040
Reportable Segments [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(72,700)	(60,137)	(125,605)	(122,799)
Civil [Member]
Business Segments [Line items]
Revenue	473,658	402,473	807,152	665,587
Income (loss) from construction operations	(164,472)	49,439	(122,727)	52,278
Capital expenditures	24,439	27,352	38,451	46,548
Depreciation and amortization	10,285	6,569	19,655	12,325
Civil [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	541,117	461,614	924,739	787,014
Civil [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(67,459)	(59,141)	(117,587)	(121,427)
Building [Member]
Business Segments [Line items]
Revenue	428,318	446,979	861,784	937,220
Income (loss) from construction operations	(3,810)	12,536	(677)	18,961
Capital expenditures	150	592	205	870
Depreciation and amortization	497	489	1,000	970
Building [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	433,559	447,975	869,802	938,592
Building [Member] | Elimination Of Intersegment Revenues [Member]
Business Segments [Line items]
Revenue	(5,241)	(996)	(8,018)	(1,372)
Specialty Contractors [Member]
Business Segments [Line items]
Revenue	223,299	270,633	414,826	545,434
Income (loss) from construction operations	(159,795)	7,454	(167,283)	14,689
Capital expenditures	110	215	233	634
Depreciation and amortization	1,061	1,106	2,125	2,218
Specialty Contractors [Member] | External And Intersegment Customers [Member]
Business Segments [Line items]
Revenue	223,299	270,633	414,826	545,434
Corporate [Member]
Business Segments [Line items]
Income (loss) from construction operations	(13,640)	(14,614)	(28,117)	(32,038)
Capital expenditures	235	174	457	251
Depreciation and amortization	$ 2,754	$ 2,813	$ 5,534	$ 5,651