Overview and Summary of Significant Accounting Policies - Unsatisfied Performance Obligation (Details) $ in Millions	Mar. 31, 2020 USD ($)
Energy Equipment Group | Wind towers and utility structures
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Unsatisfied performance obligations, Amount	$ 475.6
Revenue, remaining performance obligation expected to be delivered in next year	82.00%
Energy Equipment Group | Other
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Unsatisfied performance obligations, Amount	$ 29.0
Revenue, remaining performance obligation expected to be delivered in next year	100.00%
Transportation Products Group | Inland barge
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Unsatisfied performance obligations, Amount	$ 348.3
Revenue, remaining performance obligation expected to be delivered in next year	91.00%