Summary of Significant Accounting Policies - Unsatisfied Performance Obligations (Details) $ in Millions	Dec. 31, 2019 USD ($)
Wind towers and utility structures | Energy Equipment Group
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Unsatisfied performance obligations, Amount	$ 596.8
Unsatisfied performance obligations, Percent expected to be delivered in 2020	86.00%
Other | Energy Equipment Group
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Unsatisfied performance obligations, Amount	$ 36.2
Unsatisfied performance obligations, Percent expected to be delivered in 2020	100.00%
Inland barge | Transportation Products Group
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Unsatisfied performance obligations, Amount	$ 346.9
Unsatisfied performance obligations, Percent expected to be delivered in 2020	100.00%