Share Plans (Schedule of the Valuation Assumptions Used in the Conversion) (Details) - $ / shares	12 Months Ended
Dec. 27, 2019	Dec. 28, 2018	Dec. 29, 2017	Dec. 30, 2016
Weighted Average Assumptions
Expected share price volatility	45.80%	38.20%	36.00%
Risk-free interest rate	2.20%	2.60%	2.00%
Expected annual dividend per share	0.00%	0.00%	0.00%
Expected life of options (in years)	5 years 3 months 18 days	5 years 3 months 18 days	5 years 3 months 18 days
Fair value per option	$ 9.66	$ 5.32	$ 18.36
Share options outstanding	6,890,700	7,007,051	4,643,984	3,386,694

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Number of options outstanding, including both vested and non-vested options.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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- Definition

Expected term of 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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