Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (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 stock options		272			272
Issuance of shares upon exercise of stock options, shares	99
Issuance of shares under employee stock purchase plan		222			222
Issuance of shares under employee stock purchase plan, shares	18
Issuance of shares upon vesting of restriced stock units, shares	58
Stock-based compensation expense		5,060			5,060
Tax payments related to shares withheld for vested restricted stock units		(613)			(613)
Unrealized gain on available-for-sale securities			23		23
Net loss				(21,437)	(21,437)
Balance at Jun. 30, 2019	$ 21	146,973	22	(97,155)	49,861
Balance, shares at Jun. 30, 2019	20,768
Balance at Mar. 31, 2019	$ 21	144,887	2	(85,796)	59,114
Balance, shares at Mar. 31, 2019	20,710
Issuance of shares upon exercise of stock options
Issuance of shares upon exercise of stock options, shares	58
Stock-based compensation expense		2,699			2,699
Tax payments related to shares withheld for vested restricted stock units		(613)			(613)
Unrealized gain on available-for-sale securities			20		20
Net loss				(11,359)	(11,359)
Balance at Jun. 30, 2019	$ 21	146,973	22	(97,155)	49,861
Balance, shares at Jun. 30, 2019	20,768
Balance at Dec. 31, 2019	$ 21	153,401	4	(122,689)	$ 30,737
Balance, shares at Dec. 31, 2019	20,825				20,825
Issuance of shares upon exercise of stock options		9			$ 9
Issuance of shares upon exercise of stock options, shares	1
Issuance of shares under employee stock purchase plan		255			255
Issuance of shares under employee stock purchase plan, shares	43
Issuance of common stock and warrants in connection with rights offering, net of issuance cost of $501	$ 4	29,494			29,498
Issuance of common stock and warrants in connection with rights offering, net of issuance cost of $501, shares	4,280
Stock-based compensation expense		5,038			5,038
Unrealized gain on available-for-sale securities			(4)		(4)
Net loss				(23,205)	(23,205)
Balance at Jun. 30, 2020	$ 25	188,197		(145,894)	$ 42,328
Balance, shares at Jun. 30, 2020	25,149				25,149
Balance at Mar. 31, 2020	$ 21	156,291	17	(134,561)	$ 21,768
Balance, shares at Mar. 31, 2020	20,869
Issuance of common stock and warrants in connection with rights offering, net of issuance cost of $501	$ 4	29,494			29,498
Issuance of common stock and warrants in connection with rights offering, net of issuance cost of $501, shares	4,280
Stock-based compensation expense		2,412			2,412
Unrealized gain on available-for-sale securities			(17)		(17)
Net loss				(11,333)	(11,333)
Balance at Jun. 30, 2020	$ 25	$ 188,197		$ (145,894)	$ 42,328
Balance, shares at Jun. 30, 2020	25,149				25,149