Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets:
Allowances for accounts receivable	$ 37.0	$ 28.6
Stockholders' equity:
Preferred stock, par value (USD per share)	$ 1.00	$ 1.00
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 (USD per share)	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares, issued	67,316,487	66,590,875
Common stock, shares outstanding	65,123,505	64,397,893
Treasury stock, shares	2,192,982	2,192,982