Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Preferred Stock [Member] Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2014	98,354,541	1,541,169
Balance at Dec. 31, 2014	$ 38,213
Balance at Dec. 31, 2014		$ 2	$ 16	$ (43,135)	$ (43,117)
Reclassification from temporary equity to permanent equity (in shares)	(98,354,541)
Reclassification from temporary equity to permanent equity	$ (38,213)
Permanent equity, reclassified from temporary equity (in shares)	98,354,541
Permanent equity, reclassified from temporary equity	$ 38,213				38,213
Conversion of convertible notes (in shares)	12,075,610
Conversion of convertible notes	$ 7,781				7,781
Exercise of convertible preferred stock warrants for series D preferred shares (in shares)	67,884
Exercise of convertible preferred stock warrants for series D preferred shares	$ 34				34
Exercise of convertible preferred stock warrants for series F preferred shares (in shares)	2,479
Exercise of convertible preferred stock warrants for series F preferred shares	$ 2				2
Exercise of stock options (in shares)		37,793
Exercise of stock options			59		59
Stock-based compensation			283		283
Net loss				(6,697)	(6,697)
Balance (in shares) at Dec. 31, 2015	110,500,514	1,578,962
Balance at Dec. 31, 2015	$ 46,030	$ 2	358	(49,832)	(3,442)
Conversion of convertible notes (in shares)		8,091,103
Conversion of convertible notes		$ 8	12,148		12,156
Exercise of stock options (in shares)		13,460
Exercise of stock options			22		22
Stock-based compensation			942		942
Net loss				(10,310)	(10,310)
Exchange of convertible preferred stock warrants to common stock (in shares)		10,807
Exchange of convertible preferred stock warrants to common stock			25		25
Reclassification of convertible shareholder notes derivative liability			2,268		2,268
Conversion of preferred stock into common stock (in shares)	(110,500,514)	9,208,376
Conversion of preferred stock into common stock	$ (46,030)	$ 9	46,021
Issuance of common stock upon reverse merger (in shares)		19,228,595
Issuance of common stock upon reverse merger		$ 19	18,902		18,921
Balance (in shares) at Dec. 31, 2016		38,131,303
Balance at Dec. 31, 2016		$ 38	80,686	(60,142)	$ 20,582
Exercise of stock options (in shares)		87,357			87,542
Exercise of stock options			144		$ 144
Stock-based compensation			2,707		2,707
Net loss				(12,308)	(12,308)
Balance (in shares) at Dec. 31, 2017		38,218,660
Balance at Dec. 31, 2017		$ 38	$ 83,537	$ (72,450)	$ 11,125