Shareholders' equity - accumulated other comprehensive income (loss) into income expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 28, 2014	Jun. 29, 2014	Mar. 30, 2014	Dec. 31, 2013	Sep. 29, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold									$ 897,404		$ 857,326		$ 802,784
Total before tax									220,110		175,730		(165,369)
Taxes on income (loss) from continuing operations									28,650		23,547		16,413
Income (loss) from continuing operations	52,133	55,228	48,830	35,269	35,302	45,779	43,401	27,701	191,460		152,183		(181,782)
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications, net of tax									2,235		5,686
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax									(705)		884
Taxes on income (loss) from continuing operations									111		46
Income (loss) from continuing operations									(594)		930
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges | Commodity Contract
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold									(705)		884
Reclassification out of Accumulated Other Comprehensive Income | Pension and Other Postretirement Benefits Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax									4,364		7,195
Taxes on income (loss) from continuing operations									(1,535)		(2,439)
Income (loss) from continuing operations									2,829		4,756
Actuarial losses									4,385	[1]	7,211	[1]
Prior-service costs									(21)	[1]	(21)	[1]
Transition obligation									$ 0	[1]	$ 5	[1]

[1] These accumulated other comprehensive income components are included in the computation of net benefit cost of pension and other postretirement benefit plans (see Note 14 to the consolidated financial statements for additional information).