Pension and other postretirement benefits - amounts recognized in accumulated other comprehensive (income) loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, accumulated other comprehensive (income) loss, net of tax	$ 265,091
Impact of currency translation, accumulated other comprehensive (income) loss, net of tax	83,889	$ (173,074)	$ 69,162
Ending balance, accumulated other comprehensive (income) loss, net of tax	341,085	265,091
Pension
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, prior service cost (credit)	51	79
Net amortization and deferral, prior service cost	(17)	(28)
Settlements, prior service cost	0
Actuarial changes in benefit obligation, prior service cost	0	0
Curtailments, prior service cost (credit)	0
Impact of currency translation, prior service cost (credit)	0	0
Ending balance, prior service cost (credit)	191	51	79
Beginning balance, net (gain) or loss	209,314	209,706
Net amortization and deferral, net (gain) or loss	(6,760)	(6,706)
Settlements, net gain (loss)	(486)
Actuarial changes in benefit obligation, net gain (loss)	4,495	4,818
Curtailments, Net (Gain) or Loss	(162)
Impact of currency translation, net (gain) or loss	(682)	1,496
Ending balance, net (gain) or loss	205,719	209,314	209,706
Beginning balance, deferred taxes	(75,277)	(76,140)
Net amortization and deferral, deferred taxes	1,579	2,395
Settlements, deferred taxes	83
Actuarial changes in benefit obligation, deferred taxes	(1,012)	(1,119)
Curtailments, deferred taxes	42
Impact of currency translation, deferred taxes	183	(413)
Ending balance, deferred taxes	(74,429)	(75,277)	(76,140)
Beginning balance, accumulated other comprehensive (income) loss, net of tax	134,088	133,645
Net amortization and deferral, accumulated other comprehensive (income) loss, net of tax	(5,198)	(4,339)
Settlements, accumulated other comprehensive (income) loss, net of tax	(403)
Actuarial changes in benefit obligation, accumulated other comprehensive income (loss), net of tax	3,483	3,699
Curtailments, accumulated other comprehensive income (loss), net of tax	(120)
Impact of currency translation, accumulated other comprehensive (income) loss, net of tax	(499)	1,083
Defined benefit plan, plan amendments and prior service costs	157
Defined benefit plan, net (gain) or loss on plan amendments	0
Defined benefit plan, plan amendments on deferred taxes	(27)
Plan amendments in benefit obligation, accumulated other comprehensive income loss, net of tax	(130)
Ending balance, accumulated other comprehensive (income) loss, net of tax	131,481	134,088	133,645
Other Benefits
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, prior service cost (credit)	305	85
Net amortization and deferral, prior service cost	(77)	(77)
Actuarial changes in benefit obligation, prior service cost	0	0
Curtailments, prior service cost (credit)	(157)
Ending balance, prior service cost (credit)	71	305	85
Beginning balance, net (gain) or loss	6,410	4,330
Net amortization and deferral, net (gain) or loss	(59)	(198)
Actuarial changes in benefit obligation, net gain (loss)	(6,058)	2,278
Curtailments, Net (Gain) or Loss	0
Ending balance, net (gain) or loss	293	6,410	4,330
Beginning balance, deferred taxes	(1,995)	(1,464)
Net amortization and deferral, deferred taxes	32	101
Actuarial changes in benefit obligation, deferred taxes	1,459	(558)
Curtailments, deferred taxes	39
Ending balance, deferred taxes	(465)	(1,995)	(1,464)
Beginning balance, accumulated other comprehensive (income) loss, net of tax	4,720	2,951
Net amortization and deferral, accumulated other comprehensive (income) loss, net of tax	(104)	(174)
Actuarial changes in benefit obligation, accumulated other comprehensive income (loss), net of tax	(4,599)	1,720
Curtailments, accumulated other comprehensive income (loss), net of tax	(118)
Defined benefit plan, plan amendments and prior service costs		297
Defined benefit plan, net (gain) or loss on plan amendments		0
Defined benefit plan, plan amendments on deferred taxes		(74)
Plan amendments in benefit obligation, accumulated other comprehensive income loss, net of tax		(223)
Ending balance, accumulated other comprehensive (income) loss, net of tax	$ (101)	$ 4,720	$ 2,951