Cash, cash equivalents and short-term investments (Detail) - USD ($) $ in Thousands	Jan. 03, 2020	Dec. 28, 2018
Fair Value Measurements [Line Items]
Amortized Cost	$ 231,277	$ 208,693
Unrealized Gains	324	91
Unrealized Losses	0	(230)
Estimated Fair Value	231,601	208,554
Cash
Fair Value Measurements [Line Items]
Amortized Cost	135,225	120,846
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	135,225	120,846
Money market securities
Fair Value Measurements [Line Items]
Amortized Cost	41,211	6,213
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	41,211	6,213
Total cash equivalents
Fair Value Measurements [Line Items]
Amortized Cost	41,211	6,213
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	41,211	6,213
Total cash and cash equivalents
Fair Value Measurements [Line Items]
Amortized Cost	176,436	127,059
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	176,436	127,059
U.S. Treasury and agency securities
Fair Value Measurements [Line Items]
Amortized Cost	54,841	81,634
Unrealized Gains	324	91
Unrealized Losses	0	(230)
Estimated Fair Value	55,165	81,495
Total short-term investments
Fair Value Measurements [Line Items]
Amortized Cost	54,841	81,634
Unrealized Gains	324	91
Unrealized Losses	0	(230)
Estimated Fair Value	$ 55,165	$ 81,495

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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