Goodwill and Intangible Assets - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended				12 Months Ended
	Apr. 10, 2017	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill, impairment Loss		$ 0	$ 69,500			$ 69,483
Amortization expense				$ 658	$ 3,389
Finite-lived intangible assets, net		7,237		$ 7,237	$ 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		700
TAS Commercial Concrete
Business Acquisition [Line Items]
Business combination, indefinite-lived intangible assets		$ 6,900
Marine
Business Acquisition [Line Items]
Goodwill, impairment Loss			33,800
Concrete
Business Acquisition [Line Items]
Goodwill, impairment Loss			$ 35,700