Debt - Interest expense (Details) - USD ($) $ in Thousands	12 Months Ended
Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Interest expense related to the notes
Interest Expense, Total	$ 34,142	$ 20,233	$ 19,694
Convertible Senior Notes
Interest expense related to the notes
Contractual interest expense	5,530	5,485	5,500
Amortization of debt discount	19,375	11,717	11,202
Amortization of debt issuance costs	2,058	1,768	1,690
Interest Expense, Total	$ 26,963	$ 18,970	$ 18,392

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.

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Represents the portion of interest incurred in the period on debt arrangements that was charged against earnings, excluding amortization of debt discount (premium) and financing costs.

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