Pension and other postretirement benefits - amounts recognized in accumulated other comprehensive (income) loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, accumulated other comprehensive (income) loss, net of tax	$ 260,895	$ 110,855
Impact of currency translation, accumulated other comprehensive (income) loss, net of tax	110,671	105,410	$ 9,637
Ending balance, accumulated other comprehensive (income) loss, net of tax	371,124	260,895	110,855
Pension
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, prior service cost (credit)	148	182
Net Amortization and deferral	(35)	(34)
Actuarial gain (loss) obligation, prior service cost (credit)	0	0
Impact of currency translation, prior service cost (credit)	0	0
Ending balance, prior service cost (credit)	113	148	182
Beginning balance, net (gain) or loss	212,969	144,684
Net amortization and deferral, net (gain) or loss	(6,124)	(4,337)
Actuarial changes in benefit obligation, net gain (loss)	7,520	73,596
Impact of currency translation, net (gain) or loss	(1,177)	(974)
Ending balance, net (gain) or loss	213,188	212,969	144,684
Beginning balance, deferred taxes	(76,807)	(52,480)
Net amortization and deferral, deferred taxes	2,164	1,539
Actuarial changes in benefit obligation, deferred taxes	(2,928)	(26,131)
Impact of currency translation, deferred taxes	316	265
Ending balance, deferred taxes	(77,255)	(76,807)	(52,480)
Beginning balance, accumulated other comprehensive (income) loss, net of tax	136,310	92,386
Net amortization and deferral, accumulated other comprehensive (income) loss, net of tax	(3,995)	(2,832)
Actuarial changes in benefit obligation, accumulated other comprehensive income (loss), net of tax	4,592	47,465
Impact of currency translation, accumulated other comprehensive (income) loss, net of tax	(861)	(709)
Ending balance, accumulated other comprehensive (income) loss, net of tax	136,046	136,310	92,386
Other Benefits
Defined Benefit Plan, Chance in Amounts Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, prior service cost (credit)	72	17
Net Amortization and deferral	35	55
Actuarial gain (loss) obligation, prior service cost (credit)	0	0
Ending balance, prior service cost (credit)	107	72	17
Beginning balance, net (gain) or loss	8,281	7,056
Net amortization and deferral, net (gain) or loss	(251)	(48)
Actuarial changes in benefit obligation, net gain (loss)	(3,914)	1,273
Ending balance, net (gain) or loss	4,116	8,281	7,056
Beginning balance, deferred taxes	(2,919)	(2,422)
Net amortization and deferral, deferred taxes	78	(4)
Actuarial changes in benefit obligation, deferred taxes	1,459	(493)
Ending balance, deferred taxes	(1,382)	(2,919)	(2,422)
Beginning balance, accumulated other comprehensive (income) loss, net of tax	5,434	4,651
Net amortization and deferral, accumulated other comprehensive (income) loss, net of tax	138	(3)
Actuarial changes in benefit obligation, accumulated other comprehensive income (loss), net of tax	(2,455)	780
Ending balance, accumulated other comprehensive (income) loss, net of tax	$ 2,841	$ 5,434	$ 4,651