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 (in shares) at Dec. 28, 2014		56,182
Beginning balance at Dec. 28, 2014	$ 35,567	$ 56	$ 238,419	$ (202,908)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under stock plans and employee stock purchase plans (in shares)		722
Common stock issued under stock plans and employee stock purchase plans	554	$ 1	553
Stock-based compensation	2,052		2,052
Net loss	(17,848)			(17,848)
Ending balance (in shares) at Jan. 03, 2016		56,904
Ending balance at Jan. 03, 2016	20,325	$ 57	241,024	(220,756)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under stock plans and employee stock purchase plans (in shares)		1,230
Common stock issued under stock plans and employee stock purchase plans	424	$ 1	423
Private stock offering, net of issuance costs (in shares)		10,000
Adjustment of Common stock and Warrants issuance costs	8,803	$ 10	8,793
Stock-based compensation	1,584		1,584
Net loss	(19,148)			(19,148)
Ending balance (in shares) at Jan. 01, 2017		68,134
Ending balance at Jan. 01, 2017	11,988	$ 68	251,824	(239,904)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under stock plans and employee stock purchase plans (in shares)		1,069
Common stock issued under stock plans and employee stock purchase plans	351	$ 1	350
Private stock offering, net of issuance costs (in shares)		11,333
Adjustment of Common stock and Warrants issuance costs	15,229	$ 11	15,218
Stock-based compensation	1,441		1,441
Net loss	(14,131)			(14,131)
Ending balance (in shares) at Dec. 31, 2017		80,536
Ending balance at Dec. 31, 2017	$ 14,878	$ 80	$ 268,833	$ (254,035)