Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Receivables:
Allowance for doubtful receivables	$ 0.8	$ 0.8
Deferred tax liabilities relating to the VEBAs	$ 144.9	$ 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	21,112,701	21,037,841
Common stock, shares outstanding	18,672,017	19,313,235
Treasury stock, shares	2,440,684	1,724,606