CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings
Beginning balance at Dec. 31, 2017	$ 14,878	$ 80	$ 268,833	$ (254,035)
Beginning balance (in shares) at Dec. 31, 2017		80,536
Common stock issued under stock plans and employee stock purchase plan	(47)		(47)
Common Stock issued under stock plans and employee stock purchase plan, shares		91
Stock-based compensation	432		432
Net loss	(3,970)			(3,970)
Ending balance at Apr. 01, 2018	11,293	$ 80	269,218	(258,005)
Ending balance (in shares) at Apr. 01, 2018		80,627
Beginning balance at Dec. 31, 2017	14,878	$ 80	268,833	(254,035)
Beginning balance (in shares) at Dec. 31, 2017		80,536
Net loss	(10,714)
Ending balance at Sep. 30, 2018	19,551	$ 95	284,205	(264,749)
Ending balance (in shares) at Sep. 30, 2018		94,922
Beginning balance at Apr. 01, 2018	11,293	$ 80	269,218	(258,005)
Beginning balance (in shares) at Apr. 01, 2018		80,627
Common stock issued under stock plans and employee stock purchase plan	233		233
Common Stock issued under stock plans and employee stock purchase plan, shares		434
Common stock offering, net of issuance costs	13,903	$ 14	13,889
Common stock offering, net of issuance costs (in shares)		13,514
Stock-based compensation	479		479
Net loss	(3,484)			(3,484)
Ending balance at Jul. 01, 2018	22,424	$ 94	283,819	(261,489)
Ending balance (in shares) at Jul. 01, 2018		94,575
Common stock issued under stock plans and employee stock purchase plan	(129)	$ 1	(130)
Common Stock issued under stock plans and employee stock purchase plan, shares		347
Stock-based compensation	516		516
Net loss	(3,260)			(3,260)
Ending balance at Sep. 30, 2018	19,551	$ 95	284,205	(264,749)
Ending balance (in shares) at Sep. 30, 2018		94,922
Beginning balance at Dec. 30, 2018	17,255	$ 95	284,974	(267,814)
Beginning balance (in shares) at Dec. 30, 2018		95,513
Common stock issued under stock plans and employee stock purchase plan	740	$ 2	738
Common Stock issued under stock plans and employee stock purchase plan, shares		1,676
Stock-based compensation	951		951
Net loss	(3,476)			(3,476)
Ending balance at Mar. 31, 2019	15,470	$ 97	286,663	(271,290)
Ending balance (in shares) at Mar. 31, 2019		97,189
Beginning balance at Dec. 30, 2018	17,255	$ 95	284,974	(267,814)
Beginning balance (in shares) at Dec. 30, 2018		95,513
Net loss	(12,381)
Ending balance at Sep. 29, 2019	16,238	$ 116	296,317	(280,195)
Ending balance (in shares) at Sep. 29, 2019		116,556
Beginning balance at Mar. 31, 2019	15,470	$ 97	286,663	(271,290)
Beginning balance (in shares) at Mar. 31, 2019		97,189
Common stock issued under stock plans and employee stock purchase plan	210	$ 1	209
Common Stock issued under stock plans and employee stock purchase plan, shares		532
Common stock offering, net of issuance costs	8,025	$ 18	8,007
Common stock offering, net of issuance costs (in shares)		18,400
Stock-based compensation	791		791
Net loss	(4,634)			(4,634)
Ending balance at Jun. 30, 2019	19,862	$ 116	295,670	(275,924)
Ending balance (in shares) at Jun. 30, 2019		116,121
Common stock issued under stock plans and employee stock purchase plan	(94)		(94)
Common Stock issued under stock plans and employee stock purchase plan, shares		435
Common stock offering, net of issuance costs	(6)		(6)
Stock-based compensation	747		747
Net loss	(4,271)			(4,271)
Ending balance at Sep. 29, 2019	$ 16,238	$ 116	$ 296,317	$ (280,195)
Ending balance (in shares) at Sep. 29, 2019		116,556