CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 28, 2019		Sep. 29, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net revenue	$ 540,052		$ 889,121	$ 809,041
Cost of sales	285,462		479,680	426,947
Gross profit	254,590		409,441	382,094
Selling, general and administrative	116,811		123,188	133,601
Research and development	116,169		119,621	100,203
Impairment charges	0		0	35,207
Operating expenses	232,980		242,809	269,011
Income from operations	21,610		166,632	113,083
Interest income	15,132		11,971	6,491
Interest expense	(2,055)		(1,054)	(1,059)
Income before income taxes	34,687		177,549	118,515
Provision for (benefit from) income tax	22,910		120,744	(7,394)
Share of results of equity-method investee, net of tax	124		129	(190)
Net income	$ 11,653		$ 56,676	$ 126,099
Net income per share:
Basic (in dollars per share)	$ 0.18	[1]	$ 0.82	$ 1.78
Diluted (in dollars per share)	0.18	[1]	0.80	1.75
Common Stock, Dividends, Per Share, Declared	$ 0.48		$ 0.24	$ 0
Weighted average shares outstanding:
Basic (in shares)	65,286		69,380	70,906
Diluted (in shares)	65,948		70,419	72,063

[1] EPS for the year may not equal the sum of quarterly EPS due to changes in weighted share calculations.