CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock at Par Value	Additional Paid-In Capital	Accumulated Deficit
Beginning balance at Jan. 03, 2016	$ 20,325	$ 57	$ 241,024	$ (220,756)
Beginning balance (in shares) at Jan. 03, 2016		56,904
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under stock plans and employee stock purchase plans	424	$ 1	423
Common stock issued under stock plans and employee stock purchase plans (in shares)		1,230
Common stock offering, net of issuance costs	8,803	$ 10	8,793
Common stock offering, net of issuance costs (in shares)		10,000
Stock-based compensation	1,584		1,584
Net loss	(19,148)			(19,148)
Ending balance at Jan. 01, 2017	11,988	$ 68	251,824	(239,904)
Ending balance (in shares) at Jan. 01, 2017		68,134
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under stock plans and employee stock purchase plans	351	$ 1	350
Common stock issued under stock plans and employee stock purchase plans (in shares)		1,069
Common stock offering, net of issuance costs	15,229	$ 11	15,218
Common stock offering, net of issuance costs (in shares)		11,333
Stock-based compensation	1,441		1,441
Net loss	(14,131)			(14,131)
Ending balance at Dec. 31, 2017	14,878	$ 80	268,833	(254,035)
Ending balance (in shares) at Dec. 31, 2017		80,536
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under stock plans and employee stock purchase plans	353	$ 1	352
Common stock issued under stock plans and employee stock purchase plans (in shares)		1,463
Common stock offering, net of issuance costs	13,902	$ 14	13,888
Common stock offering, net of issuance costs (in shares)		13,514
Stock-based compensation	1,901		1,901
Net loss	(13,779)			(13,779)
Ending balance at Dec. 30, 2018	$ 17,255	$ 95	$ 284,974	$ (267,814)
Ending balance (in shares) at Dec. 30, 2018		95,513