Goodwill and Intangible Assets - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Apr. 10, 2017	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Aug. 05, 2015
Finite-Lived Intangible Assets [Line Items]
Net intangible assets, end of year		$ 7,895	$ 11,284	$ 7,900
Amortization expense		3,389	$ 4,736
Tony Bagliore Concrete, Inc. (TBC) | Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangibles acquired	$ 700
Acquired finite-lived intangible assets, useful life	7 years
Amortization expense		$ 3,400
Tony Bagliore Concrete, Inc. (TBC) | Contractual backlog
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangibles acquired	$ 100
Acquired finite-lived intangible assets, useful life	7 months
Reported Value Measurement [Member] | TAS Commercial Concrete | Trade Names
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets, Fair Value Disclosure					$ 6,900