Goodwill and Intangible Assets - Narrative (Details) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Asset	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Goodwill, impairment Loss		$ 69,500		$ 0		$ 69,483
Amortization expense	$ 662		$ 847	1,980	$ 2,541	3,389
Finite-lived intangible assets, net	$ 5,915	7,895		$ 5,915		$ 7,895
Number of infinite-lived intangible assets | Asset				1
TAS Commercial Concrete | Customer Relationships
Business Acquisition [Line Items]
Finite-lived intangibles acquired							$ 18,100
Acquired finite-lived intangible assets, useful life							8 years
Amortization expense				$ 2,000
Marine
Business Acquisition [Line Items]
Goodwill, impairment Loss		33,800
Concrete
Business Acquisition [Line Items]
Goodwill, impairment Loss		$ 35,700