Stock Based Compensation - Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Stock Based Compensation
Total stock-based compensation expense	$ 2,824	$ 2,989
Research and development expense
Stock Based Compensation
Total stock-based compensation expense	749	869
Sales and marketing expense
Stock Based Compensation
Total stock-based compensation expense	220	161
General and administrative expense
Stock Based Compensation
Total stock-based compensation expense	1,855	$ 1,959
Stock options and RSUs
Stock Based Compensation
Unrecognized stock-based compensation expense	$ 2,600
Expected weighted average period to be recognized	1 year 2 months 23 days
Minimum | Employee stock options
Estimated grant-date fair value of stock options calculated using the Black-Scholes option-pricing model
Volatility (as a percent)	150.10%	143.10%
Expected term (years)	5 years	5 years
Risk-free interest rate (as a percent)	0.30%	1.50%
Maximum | Employee stock options
Estimated grant-date fair value of stock options calculated using the Black-Scholes option-pricing model
Volatility (as a percent)	167.90%	145.90%
Expected term (years)	5 years	5 years 9 months 18 days
Risk-free interest rate (as a percent)	0.50%	1.90%