Quarterly Financial Data (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Quarterly Financial Data [Abstract]
Net sales	$ 338.0	$ 338.9	$ 344.1	$ 335.1	$ 311.3	$ 319.9	$ 328.9	$ 337.4	$ 1,356.1	$ 1,297.5		$ 1,360.1
Cost of products sold, excluding depreciation and amortization and other items	278.7	280.4	275.5	282.9	254.3	259.5	261.5	263.6	1,117.5	1,038.9		1,116.2
Unrealized losses (gains) on derivative instruments	10.4	3.6	(1.6)	(2.0)	(4.1)	(1.5)	4.2	0.7	10.4	(0.7)		(15.2)
Gross Profit	48.9	54.9	70.2	54.2	61.1	61.9	63.2	73.1
Operating income	26.8	32.6	46.4	32.1	41.6	41.6	40.1	50.0	137.9	173.3		165.9
Net income	$ 15.6	$ 15.9	$ 24.5	$ 15.8	$ 27.3	$ 25.4	$ 18.6	$ 33.5	$ 71.8	$ 104.8		$ 85.8
Net income per common share:
Basic	$ 0.88	$ 0.90	$ 1.38	$ 0.88	$ 1.48	$ 1.37	$ 0.99	$ 1.75	$ 4.02	$ 5.56		$ 4.49
Earnings per common share, Diluted:
Net income per share	$ 0.85	$ 0.85	$ 1.33	$ 0.85	$ 1.44	$ 1.34	$ 0.98	$ 1.73	$ 3.86	$ 5.44	[1]	$ 4.45	[1]

[1] The diluted weighted-average number of common shares outstanding during the periods were calculated using the treasury method.