Shareholders' equity - Change in accumulated other comprehensive income, net of tax (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Apr. 01, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 2,539,978	$ 2,430,531
Amounts reclassified from accumulated other comprehensive income	(1,765)	639
Ending Balance	2,569,878	2,560,500
Cash Flow Hedges
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	807	340
Other comprehensive income (loss) before reclassifications	(434)	1,341
Amounts reclassified from accumulated other comprehensive income	(163)	(720)
Net current-period other comprehensive income (loss)	(597)	621
Ending Balance	210	961
Pension and Other Postretirement Benefit Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(131,380)	(138,808)
Other comprehensive income (loss) before reclassifications	(122)	(478)
Amounts reclassified from accumulated other comprehensive income	1,351	1,359
Net current-period other comprehensive income (loss)	1,229	881
Ending Balance	(130,151)	(137,927)
Foreign Currency Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(210,512)	(126,623)
Other comprehensive income (loss) before reclassifications	(236)	81,188
Amounts reclassified from accumulated other comprehensive income	0	0
Net current-period other comprehensive income (loss)	(236)	81,188
Ending Balance	(210,748)	(45,435)
Accumulated Other Comprehensive (Loss) Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(341,085)	(265,091)
Other comprehensive income (loss) before reclassifications	(792)	82,051
Amounts reclassified from accumulated other comprehensive income	1,188	639
Net current-period other comprehensive income (loss)	396	82,690
Ending Balance	$ (340,689)	$ (182,401)

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount of increase (decrease) in other comprehensive income, after tax, from changes classified as other.

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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