Acquisitions and Divestitures - Narrative $ in Millions	1 Months Ended		12 Months Ended
	Jul. 31, 2017 USD ($)	Jun. 30, 2015 USD ($) facility	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Stock issued for acquisition (value)			$ 14.7
Purchase price			63.0	$ 0.0	$ 46.2
Gain recognized			$ 0.0	$ 0.0
Construction Products Group | Lightweight Aggregates Business
Business Acquisition [Line Items]
Stock issued for acquisition (shares) | shares			459,603
Stock issued for acquisition (value)			$ 14.7
Construction Products Group | Trench Shoring Products Business
Business Acquisition [Line Items]
Purchase price	$ 42.1
Texas, Mississippi, and Louisiana | Galvanizing Business | Construction Products Group
Business Acquisition [Line Items]
Number of facilities sold | facility		6
Gain recognized		$ 8.3			$ 8.3