CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Deficit	Accumulated Other Comprehensive Loss
Balance, beginning of period (in shares) at Sep. 29, 2018		100,868,250		(807,040)
Balance, beginning of period at Sep. 29, 2018	$ 208,358	$ 101	$ 424,617	$ (11,072)	$ (203,611)	$ (1,677)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to equity incentive plans (in shares)		174,453
Issuance of common stock pursuant to equity incentive plans	462	$ 0	462
Stock-based compensation expense	9,032		9,032
Net income (loss)	61,667				61,667
Change in foreign currency translation adjustment	509					509
Balance, end of period (in shares) at Dec. 29, 2018		101,042,703		(807,040)
Balance, ending of period at Dec. 29, 2018	280,028	$ 101	434,111	$ (11,072)	(141,944)	(1,168)
Balance, beginning of period (in shares) at Sep. 29, 2018		100,868,250		(807,040)
Balance, beginning of period at Sep. 29, 2018	208,358	$ 101	424,617	$ (11,072)	(203,611)	(1,677)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	38,843
Change in foreign currency translation adjustment	1,169
Balance, end of period (in shares) at Mar. 30, 2019		105,692,632		(861,354)
Balance, ending of period at Mar. 30, 2019	286,869	$ 106	463,677	$ (11,638)	(164,768)	(508)
Balance, beginning of period (in shares) at Dec. 29, 2018		101,042,703		(807,040)
Balance, beginning of period at Dec. 29, 2018	280,028	$ 101	434,111	$ (11,072)	(141,944)	(1,168)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to equity incentive plans (in shares)		4,649,929
Issuance of common stock pursuant to equity incentive plans	18,485	$ 5	18,480
Purchase of treasury stock (in shares)				(54,314)
Repurchase of common stock	(566)			$ (566)
Stock-based compensation expense	11,086		11,086
Net income (loss)	(22,824)				(22,824)
Change in foreign currency translation adjustment	660					660
Balance, end of period (in shares) at Mar. 30, 2019		105,692,632		(861,354)
Balance, ending of period at Mar. 30, 2019	286,869	$ 106	463,677	$ (11,638)	(164,768)	(508)
Balance, beginning of period (in shares) at Sep. 28, 2019		109,623,417		(1,020,775)
Balance, beginning of period at Sep. 28, 2019	280,928	$ 110	502,757	$ (13,498)	(208,377)	(64)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to equity incentive plans (in shares)		1,561,696
Issuance of common stock pursuant to equity incentive plans	7,969	$ 1	7,968
Purchase of treasury stock (in shares)				(372,149)
Repurchase of common stock	(5,078)			$ (5,078)
Stock-based compensation expense	13,204		13,204
Net income (loss)	70,775				70,775
Change in foreign currency translation adjustment	(519)					(519)
Balance, end of period (in shares) at Dec. 28, 2019		111,185,113		(1,392,924)
Balance, ending of period at Dec. 28, 2019	367,279	$ 111	523,929	$ (18,576)	(137,602)	(583)
Balance, beginning of period (in shares) at Sep. 28, 2019		109,623,417		(1,020,775)
Balance, beginning of period at Sep. 28, 2019	$ 280,928	$ 110	502,757	$ (13,498)	(208,377)	(64)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to equity incentive plans (in shares)	2,186,674
Purchase of treasury stock (in shares)	(2,536,845)
Net income (loss)	$ 18,454
Change in foreign currency translation adjustment	(950)
Balance, end of period (in shares) at Mar. 28, 2020		112,733,727		(3,884,652)
Balance, ending of period at Mar. 28, 2020	299,804	$ 113	541,937	$ (51,310)	(189,922)	(1,014)
Balance, beginning of period (in shares) at Dec. 28, 2019		111,185,113		(1,392,924)
Balance, beginning of period at Dec. 28, 2019	367,279	$ 111	523,929	$ (18,576)	(137,602)	(583)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to equity incentive plans (in shares)		1,548,614
Issuance of common stock pursuant to equity incentive plans	4,616	$ 2	4,614
Purchase of treasury stock (in shares)				(2,491,728)
Repurchase of common stock	(32,734)			$ (32,734)
Stock-based compensation expense	13,394		13,394
Net income (loss)	(52,320)				(52,320)
Change in foreign currency translation adjustment	(431)					(431)
Balance, end of period (in shares) at Mar. 28, 2020		112,733,727		(3,884,652)
Balance, ending of period at Mar. 28, 2020	$ 299,804	$ 113	$ 541,937	$ (51,310)	$ (189,922)	$ (1,014)