CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Accounts receivable, allowance for doubtful accounts	$ 4.2	$ 7.9
Shareholders' equity:
Preferred stock, shares authorized (in shares)	1,000,000	1,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	48,644,736	48,229,826
Common stock held in treasury, shares (in shares)	13,270,391	13,259,839