Derivatives, Hedging Programs and Other Financial Instruments, Narrative (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Derivative, Net Liability Position, Aggregate Fair Value	$ 12,600,000				$ 100,000				$ 12,600,000		$ 100,000
Cost of Goods and Services Sold	317,300,000	$ 323,300,000	$ 343,400,000	$ 316,700,000	$ 277,200,000	$ 256,400,000	$ 289,600,000	$ 262,700,000	1,300,700,000	[1]	1,085,900,000	[1]	$ 1,000,800,000	[1]
Margin deposits with counterparties	0								0
Customer Deposits, Current	$ 200,000								$ 200,000
Debt Instrument, Term									12 months
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months									$ (15,600,000)
Scenario, Forecast | Natural Gas Member
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage																	66.00%
Scenario, Forecast | Electricity [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage															9.00%	55.00%	54.00%
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
Derivative [Line Items]
OCI, before Reclassifications, before Tax, Attributable to Parent									$ (21,200,000)		$ 1,800,000		$ (100,000)

[1] See Note 7 for discussion of our adoption of ASU 2017-12 (as defined in Note 1) and the related reclassification of amounts previously presented in the Statements of Consolidated Income within Unrealized (gain) loss on derivative instruments and now included within Cost of products sold, excluding depreciation and amortization and other items.