Business Segments (Narrative) (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Jun. 30, 2019 USD ($) segment $ / shares	Jun. 30, 2018 USD ($) $ / shares	Dec. 31, 2018 segment
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3		3
Operating Income (Loss)	$ (341,717)	$ 54,815	$ (318,804)	$ 53,890
Net income (loss)	$ (315,439)	$ 27,896	$ (310,717)	$ 16,954
DILUTED EARNGINS (LOSS) PER COMMON SHARE | $ / shares	$ (6.38)	$ 0.49	$ (6.40)	$ 0.25
Scenario Unfavorable Adjustment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ 379,900		$ 379,900
Net income (loss)	$ 329,500		$ 329,500
DILUTED EARNGINS (LOSS) PER COMMON SHARE | $ / shares	$ 6.56		$ 6.57
Building [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (3,810)	$ 12,536	$ (677)	$ 18,961
Civil [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	(164,472)	49,439	(122,727)	52,278
Civil [Member] | Scenario Unfavorable Adjustment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)				17,800
Net income (loss)				$ 12,800
DILUTED EARNGINS (LOSS) PER COMMON SHARE | $ / shares				$ 0.25
Specialty Contractors [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	(159,795)	7,454	(167,283)	$ 14,689
Corporate [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (13,640)	$ (14,614)	$ (28,117)	$ (32,038)