Interest Expense on Convertible Senior Notes (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 29, 2019	Sep. 30, 2018	Sep. 29, 2019	Sep. 30, 2018
Debt Instrument
Contractual interest expense on the coupon	$ 1,438	$ 1,438	$ 4,313	$ 4,313
Amortization of the discount component and debt issue fees recognized as interest expense	3,699	3,520	10,961	10,431
Total interest expense on the convertible debt	$ 5,137	$ 4,958	$ 15,274	$ 14,744

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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