Quarterly Financial Data (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Quarterly Financial Data [Line Items]
Net sales	$ 314.0	$ 335.5	$ 345.2	$ 365.4	$ 317.6	$ 322.3	$ 338.8	$ 322.6	$ 1,360.1		$ 1,301.3		$ 1,079.1
Cost of products sold, excluding depreciation and amortization and other items	264.8	268.9	284.4	298.1	272.4	280.9	290.5	285.2	1,116.2		1,129.0		946.1
Unrealized (gains) losses on derivative instruments	0.1	(12.3)	0.1	(3.1)	7.9	16.8	9.5	(4.3)	(15.2)		29.9		0.7
Restructuring costs and other (benefits) charges					0	(0.3)	0	0
Gross Profit	49.1	78.9	60.7	70.4	37.3	24.9	38.8	41.7
Operating income	23.9	56.2	39.6	46.2	15.6	4.9	14.7	19.8	165.9		55.0		41.1
Net income	$ 9.1	$ 29.2	$ 21.0	$ 26.5	$ 6.1	$ 4.1	$ 4.1	$ 10.8	$ 85.8		$ 25.1		$ 12.0
Earnings per common share, Basic:
Net income per share	$ 0.48	$ 1.52	$ 1.10	$ 1.39	$ 0.33	$ 0.21	$ 0.22	$ 0.57	$ 4.49		$ 1.32		$ 0.61
Earnings per common share, Diluted:
Net income per share1	$ 0.47	$ 1.51	$ 1.09	$ 1.38	$ 0.33	$ 0.21	$ 0.22	$ 0.57	$ 4.45	[1],[2]	$ 1.32	[1],[2]	$ 0.61	[1],[2]
High
Common stock market price:
Common stock market price (based on daily closing price)	$ 61.75	$ 59.15	$ 52.57	$ 52.46	$ 49.46	$ 56.30	$ 54.62	$ 52.77
Low
Common stock market price:
Common stock market price (based on daily closing price)	$ 56.27	$ 49.42	$ 46.62	$ 46.82	$ 40.26	$ 43.71	$ 46.37	$ 45.88

[1] Diluted weighted-average number of common shares outstanding and diluted earnings per share for 2012 is based on the treasury method. Diluted weighted-average number of common shares outstanding and diluted earnings per share for 2011 and 2010 are based on the two-class method (see Note 1 and Note 14).

[2] The diluted weighted-average number of common shares outstanding and diluted earnings per share for 2012 were calculated using the treasury method. The diluted weighted-average number of common shares outstanding and diluted earnings per share for 2011 and 2010 were calculated using the two-class method (see Note 1).