Intangible Assets - Indefinite Lived Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Indefinite-lived Intangible Assets by Major Class [Line Items]
Goodwill	$ 53,799	$ 53,799
Construction [Member]
Indefinite-lived Intangible Assets by Major Class [Line Items]
Goodwill	29,260	29,260
Large Project Construction [Member]
Indefinite-lived Intangible Assets by Major Class [Line Items]
Goodwill	22,593	22,593
Construction Materials [Member]
Indefinite-lived Intangible Assets by Major Class [Line Items]
Goodwill	$ 1,946	$ 1,946