Condensed Guarantor and Non-Guarantor Financial Information, Comprehensive Income Statements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	$ 355.3	$ 343.2
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	277.8	262.0
Lower of cost or market inventory write-down	0.0	4.9
Unrealized gain on derivative instruments	(15.1)	(4.0)
Depreciation and amortization	9.6	8.7
Selling, general, administrative, research and development	23.7	26.1
Net periodic postretirement benefit cost relating to Salaried VEBA	1.1	0.8
Gain on removal of Union VEBA net assets – Note 5	(1.3)	(0.1)
Total selling, general, administrative, research and development	23.5	26.8
Total costs and expenses	295.8	298.4
Operating income	59.5	44.8
Other (expense) income:
Interest (expense) income	(5.6)	(3.7)
Other income, net	0.6	0.3
Income before income taxes	54.5	41.4
Income tax provision	(18.5)	(15.1)
Earnings in equity of subsidiaries	0.0	0.0
Net income	36.0	26.3
Comprehensive income	37.3	27.2
Consolidating Adjustments
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	(20.8)	(18.9)
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	(20.1)	(18.2)
Lower of cost or market inventory write-down		0.0
Unrealized gain on derivative instruments	0.0	0.0
Depreciation and amortization	0.0	0.0
Selling, general, administrative, research and development	(0.5)	(0.5)
Net periodic postretirement benefit cost relating to Salaried VEBA	0.0	0.0
Gain on removal of Union VEBA net assets – Note 5	0.0	0.0
Total selling, general, administrative, research and development	(0.5)	(0.5)
Total costs and expenses	(20.6)	(18.7)
Operating income	(0.2)	(0.2)
Other (expense) income:
Interest (expense) income	0.0	0.0
Other income, net	0.0	0.0
Income before income taxes	(0.2)	(0.2)
Income tax provision	2.5	2.0
Earnings in equity of subsidiaries	(43.2)	(31.7)
Net income	(40.9)	(29.9)
Comprehensive income	(42.2)	(30.8)
Parent
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	0.0	0.0
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	0.0	0.0
Lower of cost or market inventory write-down		0.0
Unrealized gain on derivative instruments	0.0	0.0
Depreciation and amortization	0.0	0.0
Selling, general, administrative, research and development	0.9	0.8
Net periodic postretirement benefit cost relating to Salaried VEBA	0.0	0.0
Gain on removal of Union VEBA net assets – Note 5	0.0	0.0
Total selling, general, administrative, research and development	0.9	0.8
Total costs and expenses	0.9	0.8
Operating income	(0.9)	(0.8)
Other (expense) income:
Interest (expense) income	(5.7)	(4.3)
Other income, net	0.0	0.0
Income before income taxes	(6.6)	(5.1)
Income tax provision	0.0	0.0
Earnings in equity of subsidiaries	42.6	31.4
Net income	36.0	26.3
Comprehensive income	37.3	27.2
Guarantor Subsidiaries
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	346.8	335.7
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	272.6	257.1
Lower of cost or market inventory write-down		4.9
Unrealized gain on derivative instruments	(15.1)	(4.0)
Depreciation and amortization	9.0	8.2
Selling, general, administrative, research and development	20.9	23.6
Net periodic postretirement benefit cost relating to Salaried VEBA	1.1	0.8
Gain on removal of Union VEBA net assets – Note 5	(1.3)	(0.1)
Total selling, general, administrative, research and development	20.7	24.3
Total costs and expenses	287.2	290.5
Operating income	59.6	45.2
Other (expense) income:
Interest (expense) income	0.1	0.6
Other income, net	0.6	0.3
Income before income taxes	60.3	46.1
Income tax provision	(20.8)	(16.9)
Earnings in equity of subsidiaries	0.6	0.3
Net income	40.1	29.5
Comprehensive income	41.4	30.3
Non-Guarantor Subsidiaries
CONDENSED CONSOLIDATING STATEMENT OF COMPREHENSIVE INCOME
Net sales	29.3	26.4
Cost of products sold:
Cost of products sold, excluding depreciation and amortization and other items	25.3	23.1
Lower of cost or market inventory write-down		0.0
Unrealized gain on derivative instruments	0.0	0.0
Depreciation and amortization	0.6	0.5
Selling, general, administrative, research and development	2.4	2.2
Net periodic postretirement benefit cost relating to Salaried VEBA	0.0	0.0
Gain on removal of Union VEBA net assets – Note 5	0.0	0.0
Total selling, general, administrative, research and development	2.4	2.2
Total costs and expenses	28.3	25.8
Operating income	1.0	0.6
Other (expense) income:
Interest (expense) income	0.0	0.0
Other income, net	0.0	0.0
Income before income taxes	1.0	0.6
Income tax provision	(0.2)	(0.2)
Earnings in equity of subsidiaries	0.0	0.0
Net income	0.8	0.4
Comprehensive income	$ 0.8	$ 0.5