Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Deemed Dividends
Deemed dividends on Series A convertible preferred stock	$ 8,900
Stock options
Stock option and incentive plans
Total compensation cost	$ 1,875	$ 1,826
Stock Options
Outstanding (in shares)	13,056,165
Outstanding, weighted-average exercise price (in dollars per share)	$ 3.25
Granted (in shares)	5,038,200
Granted (in dollars per share)	$ 2.04
Stock options \| Research and development
Stock option and incentive plans
Total compensation cost	$ 729	649
Stock options \| General and administrative
Stock option and incentive plans
Total compensation cost	1,146	1,177
Restricted stock
Stock option and incentive plans
Total compensation cost	$ 1	$ 10
Shares
Issued (in shares)	21,000	0
Outstanding (in shares)	21,000
Vested (in shares)	32,400
Restricted stock \| Minimum
Stock option and incentive plans
Vesting period	1 year
Restricted stock \| Maximum
Stock option and incentive plans
Vesting period	3 years
Restricted stock \| Research and development
Stock option and incentive plans
Total compensation cost		$ 5
Restricted stock \| General and administrative
Stock option and incentive plans
Total compensation cost	$ 1	$ 5
2005 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	0
2005 Plan \| Stock options
Stock Options
Outstanding (in shares)	327,421
2014 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	615,008
2014 Plan \| Stock options
Stock Options
Outstanding (in shares)	11,384,244
Granted (in shares)	4,749,700
2014 Plan \| Restricted stock
Shares
Outstanding (in shares)	21,000
Equity Incentive Plan, Employee Inducments \| Stock options
Stock Options
Granted (in shares)	288,500

The deemed dividends on the convertible preferred stock.

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