Stock-based compensation (Details) - Restricted stock units (RSUs) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Share Based Compensation Arrangement by Share Based Payment Award [Line Items]
Number of shares granted in period (in shares)	18	4	187	127
Weighted-average grant-date fair value (in usd per share)	$ 133.45	$ 204.35	$ 137.30	$ 237.94
Recognized stock-based compensation costs	$ 5,788	$ 13,645	$ 11,577	$ 21,593
Recognized stock-based compensation costs, net of tax	4,283	$ 10,097	8,567	$ 15,979
Pre-tax unrecognized compensation expense	$ 29,629		$ 29,629
Recognized expense over a weighted-average period (years)			1 year 8 months 12 days

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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Amount, after tax, of expense for award under share-based payment arrangement.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Net number of share options (or share units) granted during the period.

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