Convertible Debt - Interest (Details) - USD ($) $ in Thousands	3 Months Ended
Apr. 02, 2021	Mar. 27, 2020
Convertible Note due 2022
Debt Instrument [Line Items]
Contractual interest expense	$ 412
Amortization of debt discount	166
Amortization of debt issuance costs	52
Total interest expense recognized	630
Convertible Note due 2024
Debt Instrument [Line Items]
Contractual interest expense	578	$ 578
Amortization of debt discount	1,146	1,058
Amortization of debt issuance costs	156	144
Total interest expense recognized	$ 1,880	$ 1,780

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount of amortization expense attributable to debt issuance costs.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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