Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Abstract]
Net sales	$ 316.6	$ 336.4	$ 367.2	$ 371.7	$ 338.0	$ 338.9	$ 344.1	$ 335.1	$ 1,391.9	$ 1,356.1	$ 1,297.5
Cost of products sold, excluding depreciation and amortization and other items	251.0	267.3	294.8	302.3	278.7	280.4	275.5	282.9	1,115.4	1,117.5	1,038.9
Lower of cost or market inventory write-down	2.6	0.0	0.0	0.0					2.6	0.0	0.0
Unrealized loss (gain) on derivative instruments	(4.3)	1.7	1.5	4.5	10.4	3.6	(1.6)	(2.0)	3.4	10.4	(0.7)
Gross Profit	67.3	67.4	70.9	64.9	48.9	54.9	70.2	54.2
Operating income	35.2	40.5	37.0	(458.6)	26.8	32.6	46.4	32.1	(345.9)	137.9	173.3
Net income	$ 13.3	$ 22.1	$ 20.2	$ (292.2)	$ 15.6	$ 15.9	$ 24.5	$ 15.8	$ (236.6)	$ 71.8	$ 104.8
Net (loss) income per common share:
Basic (in dollars per share)	$ 0.76	$ 1.29	$ 1.19	$ (16.85)	$ 0.88	$ 0.90	$ 1.38	$ 0.88	$ (13.76)	$ 4.02	$ 5.56
Earnings per common share, Diluted:
Diluted (in dollars per share)	$ 0.73	$ 1.21	$ 1.11	$ (16.85)	$ 0.85	$ 0.85	$ 1.33	$ 0.85	$ (13.76)	$ 3.86	$ 5.44