Segment Information - Financial information for segments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 488.2	$ 410.9
Operating profit (loss)	45.1	37.3
Intersegment | Eliminations
Segment Reporting Information [Line Items]
Revenues	(1.4)	(1.7)
Operating profit (loss)	0.0	0.0
Total
Segment Reporting Information [Line Items]
Revenues	489.6	412.6
Operating profit (loss)	56.0	47.8
Corporate
Segment Reporting Information [Line Items]
Revenues	0.0	0.0
Operating profit (loss)	(10.9)	(10.5)
Construction Products Group | Total
Segment Reporting Information [Line Items]
Revenues	149.4	106.0
Operating profit (loss)	16.8	11.3
Energy Equipment Group | Total
Segment Reporting Information [Line Items]
Revenues	223.2	209.1
Operating profit (loss)	24.9	28.2
Transportation Products Group | Total
Segment Reporting Information [Line Items]
Revenues	117.0	97.5
Operating profit (loss)	14.3	8.3
Construction aggregates | Construction Products Group
Segment Reporting Information [Line Items]
Revenues	132.1	88.4
Other | Construction Products Group
Segment Reporting Information [Line Items]
Revenues	17.3	17.6
Other | Energy Equipment Group
Segment Reporting Information [Line Items]
Revenues	46.8	50.5
Wind towers and utility structures | Energy Equipment Group
Segment Reporting Information [Line Items]
Revenues	176.4	158.6
Inland barge | Transportation Products Group
Segment Reporting Information [Line Items]
Revenues	89.0	49.4
Steel components | Transportation Products Group
Segment Reporting Information [Line Items]
Revenues	$ 28.0	$ 48.1