Segment Information - Financial information for segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 434.1	$ 353.0	$ 845.0	$ 707.4
Operating profit (loss)	42.3	30.6	79.6	61.8
Intersegment | Eliminations
Segment Reporting Information [Line Items]
Revenues	(1.1)	(0.8)	(2.8)	(2.2)
Operating profit (loss)	0.0	0.0	0.0	0.0
Total
Segment Reporting Information [Line Items]
Revenues	435.2	353.8	847.8	709.6
Operating profit (loss)	55.1	38.5	102.9	77.4
Corporate
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0	0.0
Operating profit (loss)	(12.8)	(7.9)	(23.3)	(15.6)
Construction Products Group | Total
Segment Reporting Information [Line Items]
Revenues	115.6	83.9	221.6	154.1
Operating profit (loss)	17.5	17.6	28.8	30.0
Energy Equipment Group | Total
Segment Reporting Information [Line Items]
Revenues	204.3	178.4	413.4	374.7
Operating profit (loss)	25.0	8.2	53.2	25.7
Transportation Products Group | Total
Segment Reporting Information [Line Items]
Revenues	115.3	91.5	212.8	180.8
Operating profit (loss)	12.6	12.7	20.9	21.7
Construction aggregates | Construction Products Group
Segment Reporting Information [Line Items]
Revenues	93.2	61.1	181.6	113.7
Other | Construction Products Group
Segment Reporting Information [Line Items]
Revenues	22.4	22.8	40.0	40.4
Other | Energy Equipment Group
Segment Reporting Information [Line Items]
Revenues	53.3	45.4	103.8	94.2
Wind towers and utility structures | Energy Equipment Group
Segment Reporting Information [Line Items]
Revenues	151.0	133.0	309.6	280.5
Inland barge | Transportation Products Group
Segment Reporting Information [Line Items]
Revenues	66.1	42.9	115.5	73.7
Steel components | Transportation Products Group
Segment Reporting Information [Line Items]
Revenues	$ 49.2	$ 48.6	$ 97.3	$ 107.1