Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	May 01, 2020 USD ($)	Apr. 28, 2020 USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Effect of LIFO Inventory Liquidation on Income	$ 0.2	$ (3.6)
Excess of current cost over the stated LIFO value of inventory	8.4	11.9
Interest expense capitalized as construction in progress	1.0	1.6	$ 1.7
Non-cash asset impairment charges	0.5	26.1	1.4
Workers' compensation charge	0.6
Undiscounted workers' compensation liabilities	29.8	29.2
Discounted workers' compensation liabilities		$ 26.6
Discount rate used in estimating liabilities for worker compensation claims		1.75%
Accrued employee healthcare benefits	3.1	$ 3.5
Advertising costs	0.2	0.4	0.3
Research and development costs	$ 9.1	10.5	9.8
Accounting Standards Update ("ASU") No. 2016-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted	true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect	true
ASU No. 2018-15
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted	true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect	true
Change in Accounting Principle, Accounting Standards Update, Transition Option Elected [Extensible List]	us-gaap:AccountingStandardsUpdate201815ProspectiveMember
Fabricated Products | Idled Equipment
Significant Accounting Policies [Line Items]
Non-cash asset impairment charges	$ 0.5	$ 0.9	$ 1.4
Maximum
Significant Accounting Policies [Line Items]
Number of days to maturity for debt investment securities to be classified as cash and cash equivalents	90 days
Period over which accounts receivable is due, days	90 days
Minimum
Significant Accounting Policies [Line Items]
Number of days in maturity for debt investment securities to be classified as short-term investments	90 days
Period over which accounts receivable is due, days	30 days
Senior Notes Due 2025 | Senior Notes
Significant Accounting Policies [Line Items]
Debt principal amount	$ 350.0			$ 50.0	$ 300.0