Pension and other postretirement benefits - amounts recognized in accumulated other comprehensive (income) loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Curtailments, Net (Gain) or Loss	$ 0	$ (511)	$ 223
Beginning balance, accumulated other comprehensive (income) loss, net of tax	341,085
Impact of currency translation, accumulated other comprehensive (income) loss, net of tax	(4,195)	83,889	(173,074)
Ending balance, accumulated other comprehensive (income) loss, net of tax	344,392	341,085
Pension
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, prior service cost (credit)	191	51
Net amortization and deferral, prior service cost	(18)	(17)
Settlements, prior service cost	0	0
Actuarial changes in benefit obligation, prior service cost	0	0
Curtailments, prior service cost (credit)	0	0
Impact of currency translation, prior service cost (credit)	0	0
Ending balance, prior service cost (credit)	173	191	51
Beginning balance, net (gain) or loss	205,719	209,314
Net amortization and deferral, net (gain) or loss	(6,995)	(6,760)
Settlements, net gain (loss)	0	(486)
Actuarial changes in benefit obligation, net gain (loss)	15,033	4,495
Curtailments, Net (Gain) or Loss	0	(162)
Impact of currency translation, net (gain) or loss	59	(682)
Ending balance, net (gain) or loss	213,816	205,719	209,314
Beginning balance, deferred taxes	(74,429)	(75,277)
Net amortization and deferral, deferred taxes	1,631	1,579
Settlements, deferred taxes	0	83
Actuarial changes in benefit obligation, deferred taxes	(3,457)	(1,012)
Curtailments, deferred taxes	0	42
Impact of currency translation, deferred taxes	(15)	183
Ending balance, deferred taxes	(76,270)	(74,429)	(75,277)
Beginning balance, accumulated other comprehensive (income) loss, net of tax	131,481	134,088
Net amortization and deferral, accumulated other comprehensive (income) loss, net of tax	(5,382)	(5,198)
Settlements, accumulated other comprehensive (income) loss, net of tax	0	(403)
Actuarial changes in benefit obligation, accumulated other comprehensive income (loss), net of tax	11,576	3,483
Curtailments, accumulated other comprehensive income (loss), net of tax	0	(120)
Impact of currency translation, accumulated other comprehensive (income) loss, net of tax	44	(499)
Defined benefit plan, plan amendments and prior service costs	0	157
Defined benefit plan, net (gain) or loss on plan amendments	0	0
Defined benefit plan, plan amendments on deferred taxes	0	(27)
Plan amendments in benefit obligation, accumulated other comprehensive income loss, net of tax	0	130
Ending balance, accumulated other comprehensive (income) loss, net of tax	137,719	131,481	134,088
Other Benefits
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, prior service cost (credit)	71	305
Net amortization and deferral, prior service cost	(64)	(77)
Actuarial changes in benefit obligation, prior service cost	0	0
Curtailments, prior service cost (credit)		(157)
Ending balance, prior service cost (credit)	7	71	305
Beginning balance, net (gain) or loss	293	6,410
Net amortization and deferral, net (gain) or loss	65	(59)
Actuarial changes in benefit obligation, net gain (loss)	1,551	(6,058)
Curtailments, Net (Gain) or Loss		0
Ending balance, net (gain) or loss	1,909	293	6,410
Beginning balance, deferred taxes	(465)	(1,995)
Net amortization and deferral, deferred taxes	0	32
Actuarial changes in benefit obligation, deferred taxes	(360)	1,459
Curtailments, deferred taxes		39
Ending balance, deferred taxes	(825)	(465)	(1,995)
Beginning balance, accumulated other comprehensive (income) loss, net of tax	(101)	4,720
Net amortization and deferral, accumulated other comprehensive (income) loss, net of tax	1	(104)
Actuarial changes in benefit obligation, accumulated other comprehensive income (loss), net of tax	1,191	(4,599)
Curtailments, accumulated other comprehensive income (loss), net of tax		(118)
Defined benefit plan, plan amendments and prior service costs		0
Defined benefit plan, net (gain) or loss on plan amendments		0
Defined benefit plan, plan amendments on deferred taxes		0
Plan amendments in benefit obligation, accumulated other comprehensive income loss, net of tax		0
Ending balance, accumulated other comprehensive (income) loss, net of tax	$ 1,091	$ (101)	$ 4,720