Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Receivables:
Allowance for doubtful receivables	$ 0.8	$ 0.8
Deferred tax liabilities relating to the VEBAs	$ 0	$ 127.0
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	21,265,315	21,197,164
Common stock, shares outstanding	17,270,143	17,607,251
Treasury stock, shares	3,995,172	3,589,913