Goodwill and Intangible Assets - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended		12 Months Ended
	Apr. 10, 2017	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill, impairment Loss			$ 69,500		$ 0		$ 69,483
Amortization expense		$ 658		$ 847	1,318	$ 1,694	3,389
Finite-lived intangible assets, net		6,577	7,895		6,577		$ 7,895
Tony Bagliore Concrete, Inc. (TBC) | Order or Production Backlog
Business Acquisition [Line Items]
Finite-lived intangibles acquired	$ 100
Acquired finite-lived intangible assets, useful life	7 months
Tony Bagliore Concrete, Inc. (TBC) | Customer Relationships
Business Acquisition [Line Items]
Finite-lived intangibles acquired	$ 700
Acquired finite-lived intangible assets, useful life	7 years
Amortization expense					1,300
TAS Commercial Concrete
Business Acquisition [Line Items]
Business combination, indefinite-lived intangible assets		$ 6,900			$ 6,900
Marine
Business Acquisition [Line Items]
Goodwill, impairment Loss			33,800
Concrete
Business Acquisition [Line Items]
Goodwill, impairment Loss			$ 35,700