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
Stock-based compensation expense		2,361			2,361
Unrealized gain on available-for-sale securities			3		3
Net loss				(10,078)	(10,078)
Balance at Mar. 31, 2019	$ 21	144,887	2	(85,796)	59,114
Balance, shares at Mar. 31, 2019	20,710
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
Stock-based compensation expense		2,626			2,626
Unrealized gain on available-for-sale securities			13		13
Net loss				(11,872)	(11,872)
Balance at Mar. 31, 2020	$ 21	$ 156,291	$ 17	$ (134,561)	$ 21,768
Balance, shares at Mar. 31, 2020	20,869				20,869