CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
CONSOLIDATED BALANCE SHEETS
Accounts receivable, allowance for doubtful accounts	$ 18.4	$ 15.5
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, Authorized shares	5,000,000	5,000,000
Preferred stock, issued shares	0	0
Preferred stock, outstanding shares	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, Authorized shares	200,000,000	200,000,000
Common stock, Issued shares	72,342,804	72,609,540
Common stock, outstanding shares	72,342,804	72,609,540