Income taxes (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 11.6	$ 18.5	$ 11.3	$ (4.8)
Effective tax rate	86.60%	52.10%	16.40%	8.30%
One time discreet tax benefit	$ 4.6	$ 3.8	$ 13.5	$ 14.0
Estimated effective tax rate	32.10%	52.30%	32.10%	52.30%