Summary of Significant Accounting Policies (Details) (USD $) In Millions, except 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
Summary of Significant Accounting Policies
Potentially dilutive stock-based compensation awards excluded from computation of dilutive common shares									1,015,000	1,365,000	1,590,000
Earnings Per Basic Common Share
Income from continuing operations	$ 9.1	$ 9.2	$ 12.7	$ 8.9	$ 7.7	$ 6.8	$ 7.8	$ 7.0	$ 39.9	$ 29.3	$ 25.0
Distributed and undistributed amounts allocated to participating securities									(1.2)	(0.7)	(0.1)
Income from continuing operations available to common stockholders									38.7	28.6	24.9
Income (loss) from discontinued operations, net of taxes (Note 12)									4.4	(0.2)	134.1
Distributed and undistributed amounts allocated to participating securities									(0.1)		(0.6)
Net income available to common stockholders									43.0	28.4	158.4
Weighted-average basic shares outstanding									15,752,000	14,974,000	14,744,000
Basic earnings (loss) per share
Continuing operations (in dollars per share)	$ 0.56	$ 0.56	$ 0.78	$ 0.55	$ 0.49	$ 0.44	$ 0.52	$ 0.47	$ 2.46	$ 1.91	$ 1.69
Discontinued operations (in dollars per share)									$ 0.27	$ (0.01)	$ 9.05
Total Basic (in dollars per share)									$ 2.73	$ 1.90	$ 10.74
Earnings Per Diluted Common Share
Income from continuing operations	9.1	9.2	12.7	8.9	7.7	6.8	7.8	7.0	39.9	29.3	25.0
Distributed and undistributed amounts allocated to participating securities									(1.1)	(0.8)	(0.1)
Income from continuing operations available to common stockholders									38.8	28.5	24.9
Income (loss) from discontinued operations, net of taxes (Note 12)									4.4	(0.2)	134.1
Distributed and undistributed amounts allocated to participating securities									(0.1)		(0.6)
Net income available to common stockholders									43.1	28.3	158.4
Weighted-average basic shares outstanding									15,752,000	14,974,000	14,744,000
Add: Assumed incremental shares under stock-based compensation									320,000	675,000	768,000
Weighted-average diluted shares									16,072,000	15,649,000	15,512,000
Diluted earnings (loss) per share
Continuing operations (in dollars per share)	$ 0.55	$ 0.55	$ 0.77	$ 0.54	$ 0.47	$ 0.42	$ 0.49	$ 0.45	$ 2.41	$ 1.82	$ 1.61
Discontinued operations (in dollars per share)									$ 0.27	$ (0.01)	$ 8.60
Total Diluted (in dollars per share)									$ 2.68	$ 1.81	$ 10.21
Cash and cash equivalents
Restricted cash and cash equivalent					7.0					7.0
Inventories
FIFO value of inventories valued on the LIFO method	91.8				59.1				91.8	59.1
Supplemental retirement contribution plan
Cash and cash equivalents
Restricted cash and cash equivalent					7.0					7.0
Postretirement benefits
Cash and cash equivalents
Restricted cash and cash equivalent	$ 0.7				$ 0.6				$ 0.7	$ 0.6