Shareholders' equity - accumulated other comprehensive income (loss) into income expense (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Oct. 01, 2017	Jul. 02, 2017	Apr. 02, 2017	Dec. 31, 2016	Sep. 25, 2016	Jun. 26, 2016	Mar. 27, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold									$ 974,501	$ 871,827	$ 865,287
Income from continuing operations before taxes									284,911	245,725	244,646
Taxes on income from continuing operations									(129,648)	(8,074)	(7,838)
Income from continuing operations	$ (42,847)	$ 79,398	$ 78,363	$ 40,349	$ 60,876	$ 66,200	$ 59,395	$ 51,180	155,263	237,651	236,808
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications, net of tax									4,502	8,013	4,616
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]
Income from continuing operations before taxes									(95)	4,511	679
Taxes on income from continuing operations									84	(1,010)	(196)
Income from continuing operations									(11)	3,501	483
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									(95)	4,511	679
Reclassification out of Accumulated Other Comprehensive Income | Pension and Other Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income from continuing operations before taxes									7,009	7,021	6,375
Taxes on income from continuing operations									(2,496)	(2,509)	(2,242)
Income from continuing operations									4,513	4,512	4,133
Actuarial losses									6,904	6,965	6,375
Prior-service credits									$ 105	$ 56	$ 0