Pension and other postretirement benefits - amounts recognized in accumulated other comprehensive (income) loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, accumulated other comprehensive (income) loss, net of tax	$ 371,124	$ 260,895
Impact of currency translation, accumulated other comprehensive (income) loss, net of tax	69,162	110,671	$ 105,410
Ending balance, accumulated other comprehensive (income) loss, net of tax	438,717	371,124	260,895
Pension
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, prior service cost (credit)	113	148
Net Amortization and deferral	(34)	(35)
Actuarial gain (loss) obligation, prior service cost (credit)	0	0
Curtailments, prior service cost (credit)	0
Impact of currency translation, prior service cost (credit)	0	0
Ending balance, prior service cost (credit)	79	113	148
Beginning balance, net (gain) or loss	213,188	212,969
Net amortization and deferral, net (gain) or loss	(6,533)	(6,124)
Actuarial changes in benefit obligation, net gain (loss)	4,481	7,520
Curtailments, Net (Gain) or Loss	(23)
Impact of currency translation, net (gain) or loss	(1,407)	(1,177)
Ending balance, net (gain) or loss	209,706	213,188	212,969
Beginning balance, deferred taxes	(77,255)	(76,807)
Net amortization and deferral, deferred taxes	2,339	2,164
Actuarial changes in benefit obligation, deferred taxes	(1,603)	(2,928)
Curtailments, deferred taxes	6
Impact of currency translation, deferred taxes	373	316
Ending balance, deferred taxes	(76,140)	(77,255)	(76,807)
Beginning balance, accumulated other comprehensive (income) loss, net of tax	136,046	136,310
Net amortization and deferral, accumulated other comprehensive (income) loss, net of tax	(4,228)	(3,995)
Actuarial changes in benefit obligation, accumulated other comprehensive income (loss), net of tax	2,878	4,592
Curtailments, accumulated other comprehensive income (loss), net of tax	(17)
Impact of currency translation, accumulated other comprehensive (income) loss, net of tax	(1,034)	(861)
Ending balance, accumulated other comprehensive (income) loss, net of tax	133,645	136,046	136,310
Other Benefits
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, prior service cost (credit)	107	72
Net Amortization and deferral	(22)	35
Actuarial gain (loss) obligation, prior service cost (credit)	0	0
Ending balance, prior service cost (credit)	85	107	72
Beginning balance, net (gain) or loss	4,116	8,281
Net amortization and deferral, net (gain) or loss	(432)	(251)
Actuarial changes in benefit obligation, net gain (loss)	646	(3,914)
Ending balance, net (gain) or loss	4,330	4,116	8,281
Beginning balance, deferred taxes	(1,382)	(2,919)
Net amortization and deferral, deferred taxes	170	78
Actuarial changes in benefit obligation, deferred taxes	(252)	1,459
Ending balance, deferred taxes	(1,464)	(1,382)	(2,919)
Beginning balance, accumulated other comprehensive (income) loss, net of tax	2,841	5,434
Net amortization and deferral, accumulated other comprehensive (income) loss, net of tax	(284)	(138)
Actuarial changes in benefit obligation, accumulated other comprehensive income (loss), net of tax	394	(2,455)
Ending balance, accumulated other comprehensive (income) loss, net of tax	$ 2,951	$ 2,841	$ 5,434