Condensed Consolidated Balance Sheets (Parenthetical) (USD $)
In Millions, except Share data, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Accounts receivable, allowance for doubtful accounts (in dollars) $ 1.5 $ 0.5
Property and equipment, accumulated depreciation (in dollars) 985.8 1,095.5
Intangible assets, accumulated amortization (in dollars) $ 22.1 $ 19.5
Common stock, par value (in dollars per share) $ 0.001 $ 0.001
Common stock, shares authorized 250,000,000 250,000,000
Common stock, shares issued 76,500,000 76,100,000
Common stock, shares outstanding 72,500,000 73,200,000
Treasury stock, shares 4,000,000 2,900,000
Series A Convertible Preferred Stock    
Preferred stock, par value (in dollars per share) $ 0.001 $ 0.001
Preferred stock, shares authorized 80,000 80,000
Preferred stock, shares issued 80,000 80,000