Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Receivables:
Allowance for doubtful receivables	$ 0.8	$ 0.8
Deferred tax liabilities relating to the VEBAs	$ 139.5	$ 136.9
Stockholders' equity:
Preferred Stock, Shares Authorized	5,000,000	5,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	90,000,000	90,000,000
Common Stock, Shares, Issued	21,093,816	21,037,841
Common stock, shares issued and outstanding	19,109,614	19,313,235
Treasury stock, shares	1,984,202	1,724,606