Stock Based Compensation - Stock Compensation Expense, Restricted Stock Units (Details) - Restricted stock - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock compensation expense	$ 0	$ 0	$ 0	$ 0
Series D Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock compensation expense	0	29,000	33,000	55,000
Series D Preferred Stock | Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock compensation expense	0	14,000	17,000	28,000
Series D Preferred Stock | Sales, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock compensation expense	$ 0	$ 15,000	$ 16,000	$ 27,000