Goodwill and Other Intangible Assets (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill	$ 585,006	$ 585,006	$ 585,000
Amortization expense	3,500	3,700	13,500
Finite-Lived intangible assets
2017	3,500
2018	3,500
2019	3,500
2020	3,500
2021	3,500
Civil [Member]
Goodwill	415,300	415,300	415,300
Accumulated Impairment	76,700	76,700	76,700
Building [Member]
Goodwill	13,500	13,500	13,500
Accumulated Impairment	411,300	411,300	411,300
Specialty Contractors [Member]
Goodwill	156,200	156,200	$ 156,200
Trade Names [Member]
Indefinite-lived intangible assets
Indefinite-lived intangible assets, carrying value	50,400	50,400
Trade Names [Member]
Finite-Lived intangible assets
Finite-lived intangible assets, gross carrying value	51,100	51,100
Accumulated Amortization	$ 13,800	11,300
Weighted Average Amortization Period	20 years
Customer Relationships [Member]
Finite-Lived intangible assets
Finite-lived intangible assets, gross carrying value	$ 23,200	23,200
Accumulated Amortization	$ 17,900	$ 16,800
Weighted Average Amortization Period	12 years