Net Loss Per Share Available to Common Stockholders - Schedule of basic and diluted net loss per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 31, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss available to common stockholders	$ (452)	$ 4,099	$ (9,441)	$ (6,649)	$ (7,452)	$ (9,342)	$ (7,396)	$ (5,696)	$ (12,443)	$ (29,886)	$ (30,384)
Denominator:
Weighted average common shares outstanding—basic									42,274,777	6,287,172	5,457,629
Dilutive effect of stock equivalents resulting from stock options, RSUs, common stock warrants, preferred stock warrants and convertible preferred stock (as converted) (in shares)									0	0	0
Weighted average common shares outstanding—diluted									42,274,777	6,287,172	5,457,629
Net loss per share available to common stockholders—basic and diluted (in dollars per share)									$ (0.29)	$ (4.75)	$ (5.57)