Commitments and Contingencies (Textuals) (Details) $ in Millions		12 Months Ended			18 Months Ended
	Mar. 01, 2019 USD ($) ft²	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Deferred income		$ 10.1	$ 10.2		$ 10.2
Expense for known and future asbestos-related litigation		5.6	3.1	$ 4.0
Area of leased office building (in square feet) | ft²	192,000
Purchase price of property at end of lease term	$ 41.2
Percentage of lease balance as final payment end of lease term	87.00%
Debt covenant, debt not paid when due	$ 75.0
Insurance recoveries received		0.0	243.2	$ 124.3	367.5
Marshalltown Wind Storm [Member]
Loss Contingencies [Line Items]
Insurance recoveries received		6.6
Other Current Liabilities [Member]
Loss Contingencies [Line Items]
Deferred income		10.1	10.2		10.2
Other Noncurrent Liabilities [Member]
Loss Contingencies [Line Items]
Deferred income		$ 27.9	$ 22.1		$ 22.1