Income Taxes - Reconciliation of Effective Tax Rates (Detail)	12 Months Ended
Oct. 02, 2020	Sep. 27, 2019	Sep. 28, 2018
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	21.00%	24.50%
Change in valuation allowance	(60.50%)	(2.40%)	34.00%
Provision to return adjustments	25.40%	0.30%	8.30%
Research and development credits	20.70%	1.40%	9.00%
Global Intangible Low Taxed Income	(11.40%)	(2.90%)	0.00%
Foreign rate differential	9.10%	1.60%	5.10%
Warrant liability	(6.50%)	0.00%	4.40%
Intra-entity license transfer	(4.60%)	9.40%	0.00%
Nondeductible compensation expense	(4.10%)	(0.60%)	1.40%
State taxes net of federal benefit	0.90%	0.90%	0.80%
Section 382 adjustment	0.00%	(19.30%)	0.00%
Nondeductible legal fees	0.00%	0.00%	0.90%
2017 tax reform	0.00%	0.00%	(73.70%)
Other permanent differences	(0.90%)	(0.10%)	(0.90%)
Effective income tax rate	(10.90%)	9.30%	13.80%

Effective Income Tax Rate Reconciliation Global Low-taxed Intangible Income

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Effective Income Tax Rate Reconciliation, Inter-entity Transfer, Percent

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Effective Income Tax Rate Reconciliation Provision To Return Adjustments

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Effective income tax rate reconciliation research and development credit and domestic manufacturing deduction.

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Effective Income Tax Rate Reconciliation Section 382 Adjustment, Percent

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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