Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Allowances for accounts receivable	$ 4.5	$ 7.1
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)	76,733,599	76,191,958
Common stock, shares outstanding (in shares)	73,720,456	73,178,815
Treasury stock, shares (in shares)	3,013,143	3,013,143