Income Taxes - Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Oct. 03, 2020	Sep. 28, 2019	Sep. 29, 2018	Sep. 30, 2017
Deferred tax assets
Accrued expenses and reserves	$ 12,014	$ 12,582
Deferred revenue	11,831	11,185
U.S. net operating loss carryforwards	8,242	15,112
Foreign net operating loss carryforwards	12,183	3,414
Tax credit carryforwards	53,543	43,411
Stock-based compensation	11,018	10,368
Right-of-Use Liability	14,377	0
Amortization	7,648	4,131
Depreciation	1,101	672
Other	603	453
Total deferred tax assets	132,560	101,328
Valuation allowance	(113,939)	(95,088)	$ (72,380)	$ (94,956)
Deferred tax assets, net of valuation allowance	18,621	6,240
Deferred tax liabilities
Tax accounting method change	(2,946)	(5,086)
Right-of-Use Asset	9,914	0
Amortization	(6,093)	0
Depreciation	(187)	0
Other	(115)	0
Total deferred tax liabilities	(19,255)	(5,086)
Net deferred tax assets (liabilities)	(634)
Net deferred tax assets (liabilities)		1,154
Deferred tax assets	1,800	1,154
Deferred tax liabilities	$ (2,434)	$ 0