Pension and other postretirement benefits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Increase trend rate by 1%, increase the benefit obligation	$ 2.4
Increase trend rate by 1%, increase the benefit expenses	0.1
Decrease trend rate by 1%, decrease the benefit obligation	2.2
Decrease trend rate by 1%, decrease the benefit expenses	0.1
Defined benefit plans, annual average Medicare part D subsidy	0.2
Defined contribution plans, costs	$ 15.6	$ 12.5	$ 12.0
Equity Securities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage of securities	40.00%
Fixed Income Securities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage of securities	50.00%
Other Securities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage of securities	10.00%
Pension
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.30%	3.60%
Rate of return	7.80%	8.10%	8.10%
Accumulated benefit obligation	$ 415.9	$ 461.6
Expected employer contribution for year 2016	12.7
Accumulated other comprehensive income expected to be recognized over the next fiscal year for the Company's pension and postretirement benefit plans	$ 6.8
Postretirement Health Care Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.20%	3.60%
Expected employer contribution for year 2016	$ 4.0
Accumulated other comprehensive income expected to be recognized over the next fiscal year for the Company's pension and postretirement benefit plans	$ 0.1
Minimum
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Effective average duration to maintain	3 years
Maximum
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Effective average duration to maintain	10 years
United States | Pension
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.43%
Rate of return	8.00%	8.25%
United States | Postretirement Health Care Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.22%
Foreign Plan | Pension
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets with accumulated benefit obligation in excess of plan assets	$ 2.8	$ 1.6