Statement of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 71,042	$ 177	$ 291,908	$ (221,043)
Beginning balance, shares at Dec. 31, 2018		17,744
Share-based awards and options exercises	1,407	$ 5	1,402
Share-based awards and options exercises, shares		483
Share-based compensation expense	501		501
Net loss	(7,529)			(7,529)
Ending balance at Mar. 31, 2019	65,421	$ 182	293,811	(228,572)
Ending balance, shares at Mar. 31, 2019		18,227
Beginning balance at Dec. 31, 2018	71,042	$ 177	291,908	(221,043)
Beginning balance, shares at Dec. 31, 2018		17,744
Net loss	(21,490)
Ending balance at Sep. 30, 2019	54,330	$ 186	296,677	(242,533)
Ending balance, shares at Sep. 30, 2019		18,602
Beginning balance at Mar. 31, 2019	65,421	$ 182	293,811	(228,572)
Beginning balance, shares at Mar. 31, 2019		18,227
Share-based awards and options exercises	470	$ 2	468
Share-based awards and options exercises, shares		218
Share-based compensation expense	1,022		1,022
Net loss	(7,094)			(7,094)
Ending balance at Jun. 30, 2019	59,819	$ 184	295,301	(235,666)
Ending balance, shares at Jun. 30, 2019		18,445
Share-based awards and options exercises	443	$ 2	441
Share-based awards and options exercises, shares		157
Share-based compensation expense	935		935
Net loss	(6,867)			(6,867)
Ending balance at Sep. 30, 2019	54,330	$ 186	296,677	(242,533)
Ending balance, shares at Sep. 30, 2019		18,602
Beginning balance at Dec. 31, 2019	47,852	$ 186	297,753	(250,087)
Beginning balance, shares at Dec. 31, 2019		18,645
Share-based awards and options exercises	76	$ 1	75
Share-based awards and options exercises, shares		81
Share-based compensation expense	1,196		1,196
Net loss	(12,613)			(12,613)
Ending balance at Mar. 31, 2020	36,511	$ 187	299,024	(262,700)
Ending balance, shares at Mar. 31, 2020		18,726
Beginning balance at Dec. 31, 2019	47,852	$ 186	297,753	(250,087)
Beginning balance, shares at Dec. 31, 2019		18,645
Net loss	(23,796)
Ending balance at Sep. 30, 2020	27,478	$ 189	301,172	(273,883)
Ending balance, shares at Sep. 30, 2020		18,959
Beginning balance at Mar. 31, 2020	36,511	$ 187	299,024	(262,700)
Beginning balance, shares at Mar. 31, 2020		18,726
Share-based awards and options exercises	48	$ 1	47
Share-based awards and options exercises, shares		83
Share-based compensation expense	646		646
Net loss	(7,765)			(7,765)
Ending balance at Jun. 30, 2020	29,440	$ 188	299,717	(270,465)
Ending balance, shares at Jun. 30, 2020		18,809
Share-based awards and options exercises	410	$ 1	409
Share-based awards and options exercises, shares		150
Share-based compensation expense	1,046		1,046
Net loss	(3,418)			(3,418)
Ending balance at Sep. 30, 2020	$ 27,478	$ 189	$ 301,172	$ (273,883)
Ending balance, shares at Sep. 30, 2020		18,959