Goodwill and Intangible Assets (Changes in Carrying Amount of Goodwill) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Balance at beginning of period		$ 585,006
Gross goodwill			$ 1,072,991
Accumulated Impairment		(867,800)	(487,985)
Goodwill impairment		(379,863)
Balance at end of period	[1]	205,143
Civil [Member]
Goodwill [Line Items]
Balance at beginning of period		415,358
Gross goodwill			492,074
Accumulated Impairment			(76,716)
Goodwill impairment		(210,215)
Balance at end of period	[1]	205,143
Building [Member]
Goodwill [Line Items]
Balance at beginning of period		13,455
Gross goodwill			424,724
Accumulated Impairment			(411,269)
Goodwill impairment		(13,455)
Specialty Contractors [Member]
Goodwill [Line Items]
Balance at beginning of period		156,193
Gross goodwill			$ 156,193
Goodwill impairment		$ (156,193)

[1] As of December 31, 2019, accumulated impairment was $867.8 million.