Convertible Notes, Other Debts And Finance Leases - 2024 Convertible Notes Roll Forward (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 25, 2020	Dec. 31, 2019	Sep. 27, 2019
Debt Instrument [Line Items]
Carrying amount	$ 128,018	$ 88,629
Convertible Note due 2024
Debt Instrument [Line Items]
Principal amount	115,500	115,500	$ 115,500
Less: Debt discount, net of amortization	(20,415)	(23,652)
Less: Debt issuance costs, net of amortization	(2,776)	(3,219)
Carrying amount	$ 92,309	$ 88,629
Remaining amortization period (years)	3 years 10 months 24 days	4 years 8 months 12 days
Effective interest rate on liability component	7.95%	7.95%

Carrying amount of long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months or greater than the normal operating cycle, if longer. The debt is convertible into another form of financial instrument, typically the entity's common stock.

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Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Face (par) amount of debt instrument at time of issuance.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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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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No definition available.

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Amount, after accumulated amortization, of debt discount.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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