Pension and other postretirement benefits - Additional Information (Detail) - USD ($) $ in Millions	2 Months Ended	12 Months Ended
	Feb. 20, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Increase trend rate by 1%, increase the benefit expenses		$ 0.2
Increase trend rate by 1%, increase the benefit obligation		3.8
Decrease trend rate by 1%, decrease the benefit expenses		0.2
Decrease trend rate by 1%, decrease the benefit obligation		3.3
Defined benefit plans, annual average Medicare part D subsidy		0.2
Defined contribution plans, costs		$ 12.6	$ 11.5	$ 12.1
Equity Securities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage of securities		45.00%
Fixed Income Securities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage of securities		35.00%
Other Securities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Target allocation percentage of securities		20.00%
United States Pension Plan of US Entity, Defined Benefit
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		4.63%
Rate of return	8.25%	8.50%
United States Postretirement Benefit Plans of US Entity, Defined Benefit
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		4.31%
Pension
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		4.50%	4.10%
Rate of return		8.10%	8.30%	8.30%
Accumulated benefit obligation		$ 421.2	$ 447.4
Expected employer contribution for year 2016		$ 2.4
Postretirement Health Care Plans
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		4.30%	4.00%
Expected employer contribution for year 2016		$ 3.3