Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Allowances for accounts receivable	$ 6.7	$ 2.9
Stockholders’ equity:
Preferred stock, par value (USD per share)	$ 1.00	$ 1.00
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (USD per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	187,500,000	187,500,000
Common stock, shares, issued (in shares)	75,791,437	73,212,545
Common stock, shares outstanding (in shares)	72,778,294	71,019,563
Treasury stock, shares (in shares)	3,013,143	2,192,982