CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Deficit	Accumulated Other Comprehensive Loss
Redeemable convertible preferred stock, beginning balance (in shares) at Sep. 30, 2017	32,482,590
Redeemable convertible preferred stock, beginning balance at Sep. 30, 2017	$ 90,341
Redeemable convertible preferred stock, ending balance (in shares) at Jun. 30, 2018	32,482,590
Redeemable convertible preferred stock, ending balance at Jun. 30, 2018	$ 90,341
Balance, beginning of period (in shares) at Sep. 30, 2017		59,339,336		(746,462)
Balance, beginning of period at Sep. 30, 2017	27	$ 59	$ 200,301	$ (10,161)	$ (188,007)	$ (2,165)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to equity incentive plans (in shares)		1,735,750
Issuance of common stock pursuant to equity incentive plans	5,748	$ 2	5,746
Purchase of treasury stock (in shares)				(60,578)
Purchase of treasury stock	(911)			$ (911)
Stock-based compensation expense	29,397		29,397
Net loss	(13,884)				(13,884)
Change in foreign currency translation adjustment	523
Balance, end of period (in shares) at Jun. 30, 2018		61,075,086		(807,040)
Balance, ending of period at Jun. 30, 2018	$ 20,900	$ 61	235,444	$ (11,072)	(201,891)	(1,642)
Redeemable convertible preferred stock, beginning balance (in shares) at Mar. 31, 2018	32,482,590
Redeemable convertible preferred stock, beginning balance at Mar. 31, 2018	$ 90,341
Redeemable convertible preferred stock, ending balance (in shares) at Jun. 30, 2018	32,482,590
Redeemable convertible preferred stock, ending balance at Jun. 30, 2018	$ 90,341
Balance, beginning of period (in shares) at Mar. 31, 2018		60,707,232		(799,174)
Balance, beginning of period at Mar. 31, 2018	36,121	$ 61	223,720	$ (10,953)	(174,903)	(1,804)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to equity incentive plans (in shares)		367,854
Issuance of common stock pursuant to equity incentive plans	1,391	$ 0	1,391
Purchase of treasury stock (in shares)				(7,866)
Purchase of treasury stock	(119)			$ (119)
Stock-based compensation expense	10,333		10,333
Net loss	(26,988)				(26,988)
Change in foreign currency translation adjustment	162					162
Balance, end of period (in shares) at Jun. 30, 2018		61,075,086		(807,040)
Balance, ending of period at Jun. 30, 2018	20,900	$ 61	235,444	$ (11,072)	(201,891)	(1,642)
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)	5,869,451	6,305,429		0
Issuance of common stock pursuant to equity incentive plans	$ 22,034	$ 6	22,028
Purchase of treasury stock (in shares)				(79,879)
Purchase of treasury stock	(832)			$ (832)
Stock-based compensation expense	33,525		33,525
Net loss	24,834				24,834
Change in foreign currency translation adjustment	506
Balance, end of period (in shares) at Jun. 29, 2019		107,173,679		(886,919)
Balance, ending of period at Jun. 29, 2019	288,425	$ 107	480,170	$ (11,904)	(178,777)	(1,171)
Balance, beginning of period (in shares) at Mar. 30, 2019		105,692,632		(861,354)
Balance, beginning of period at Mar. 30, 2019	286,869	$ 106	463,677	$ (11,638)	(164,768)	(508)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock pursuant to equity incentive plans (in shares)		1,481,047
Issuance of common stock pursuant to equity incentive plans	3,086	$ 1	3,085
Purchase of treasury stock (in shares)				(25,565)
Purchase of treasury stock	(266)			$ (266)
Stock-based compensation expense	13,408		13,408
Net loss	(14,009)				(14,009)
Change in foreign currency translation adjustment	(663)					(663)
Balance, end of period (in shares) at Jun. 29, 2019		107,173,679		(886,919)
Balance, ending of period at Jun. 29, 2019	$ 288,425	$ 107	$ 480,170	$ (11,904)	$ (178,777)	$ (1,171)