Summary of Significant Accounting Policies, Narrative (Details) $ in Millions		12 Months Ended
	Jan. 01, 2018 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Accounting policies additional disclosures
Number of operating segments | segment		1
Advertising costs		$ 0.3	$ 0.7	$ 0.4
Research and development costs		9.8	10.0	10.2
Lower of cost or market inventory write-down		0.0	0.0	4.9
Excess of current cost over the stated LIFO value of inventory		31.7	24.3
Non-cash asset impairment charges		1.4	19.2	$ 2.8
Undiscounted workers' compensation liabilities		$ 27.6	$ 24.8
Discount rate used in estimating liabilities for worker compensation claims		3.00%	2.25%
Accrued employee healthcare benefits		$ 3.6	$ 3.5
Retained earnings	$ 95.6	$ 150.2	$ 85.5
Minimum
Accounting policies additional disclosures
Period over which accounts receivable is due, days		30 days
Number of days in maturity for debt investment securities to be classified as short-term investments		90 days
Maximum
Accounting policies additional disclosures
Period over which accounts receivable is due, days		90 days
Number of days to maturity for debt investment securities to be classified as cash and cash equivalents		90 days
Scenario, Forecast | Accounting Standards Update 2016-02 | Minimum
Accounting policies additional disclosures
Right-of-use asset					$ 20.0
Lease liability					20.0
Scenario, Forecast | Accounting Standards Update 2016-02 | Maximum
Accounting policies additional disclosures
Right-of-use asset					30.0
Lease liability					$ 30.0
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09
Accounting policies additional disclosures
Tax impact of cumulative increase to retained earnings	(3.3)
Retained earnings	10.1	$ (15.5)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2016-01
Accounting policies additional disclosures
Retained earnings	$ 0.6