Income taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Components of income tax expenses (benefit)
Current income tax expense	$ 1.2	$ 1.6	$ 2.4	$ 2.9
Deferred income tax expense (benefit)			0.3	(0.7)
Total income tax expense, net	$ 1.2	$ 1.6	$ 2.7	$ 2.2