Net loss per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net loss	$ (12.5)	$ (26.0)
Denominator:
Weighted-average number of shares-basic (in shares)	52.0	51.2
Dilutive securities-equity awards (in shares)	0.0	0.0
Weighted-average number of shares-diluted (in shares)	52.0	51.2
Net loss per share - basic (in dollars per share)	$ (0.24)	$ (0.51)
Net loss per share - diluted (in dollars per share)	$ (0.24)	$ (0.51)
Antidilutive securities excluded from computation of earnings per share	0.7	3.1