Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Total
Balance at Dec. 31, 2018	$ 21	$ 142,032	$ (1)	$ (75,718)	$ 66,334
Balance, shares at Dec. 31, 2018	20,593
Issuance of shares upon exercise of warrants, shares	37
Issuance of shares upon exercise of stock options		272			272
Issuance of shares upon exercise of stock options, shares	99
Issuance of shares under employee stock purchase plan		423			423
Issuance of shares under employee stock purchase plan, shares	38
Issuance of common stock upon vesting of restricted stock units, net of shares withheld for employee taxes, shares	58
Stock-based compensation expense		11,287			11,287
Tax payments related to shares withheld for vested restricted stock units		(613)			(613)
Unrealized gain on available-for-sale securities			5		5
Net loss				(46,971)	(46,971)
Balance at Dec. 31, 2019	$ 21	153,401	4	(122,689)	30,737
Balance, shares at Dec. 31, 2019	20,825
Issuance of shares upon exercise of warrants		1,127			1,127
Issuance of shares upon exercise of warrants, shares	187
Issuance of shares upon exercise of stock options		887			887
Issuance of shares upon exercise of stock options, shares	175
Issuance of shares under employee stock purchase plan		490			490
Issuance of shares under employee stock purchase plan, shares	83
Issuance of common stock and warrants in connection with rights offering at $7.01 per unit, net of issuance cost of $565	$ 4	29,430			29,434
Issuance of common stock and warrants in connection with rights offering at $7.01 per unit, net of issuance cost of $565, shares	4,280
Stock-based compensation expense		10,075			10,075
Unrealized gain on available-for-sale securities			(5)		(5)
Net loss				(49,851)	(49,851)
Balance at Dec. 31, 2020	$ 25	195,410	(1)	(172,540)	$ 22,894
Balance, shares at Dec. 31, 2020	25,550				25,550
Issuance of common stock as part of debt extinguishment and private investment, net of issuance cost of $106	$ 3	49,891			$ 49,894
Issuance of common stock as part of debt extinguishment and private investment, net of issuance cost of $106, shares	3,049
Issuance of shares upon exercise of warrants	$ 1	3,333			3,334
Issuance of shares upon exercise of warrants, shares	585
Issuance of shares upon exercise of stock options		616			616
Issuance of shares upon exercise of stock options, shares	54
Issuance of common stock as part of ATM offering, net of issuance cost of $568		7,432			7,432
Issuance of common stock as part of ATM offering net of issuance cost of $568, shares	288
Issuance of shares under employee stock purchase plan		810			810
Issuance of shares under employee stock purchase plan, shares	91
Issuance of common stock upon vesting of restricted stock units, net of shares withheld for employee taxes		(232)			(232)
Issuance of common stock upon vesting of restricted stock units, net of shares withheld for employee taxes, shares	99
Stock-based compensation expense		14,601			14,601
Unrealized gain on available-for-sale securities			$ 1		1
Net loss				(63,660)	(63,660)
Balance at Dec. 31, 2021	$ 29	$ 271,861		$ (236,200)	$ 35,690
Balance, shares at Dec. 31, 2021	29,716				29,716