Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock options
Stock option and incentive plans
Total compensation cost	$ 1,329	$ 1,153	$ 4,408	$ 3,576
Stock Options
Outstanding (in shares)	8,431,488		8,431,488
Outstanding, weighted-average exercise price (in dollars per share)	$ 4.13		$ 4.13
Granted (in shares)	4,082,000		4,082,000
Granted (in dollars per share)	$ 2.45		$ 2.45
Stock options | Research and development
Stock option and incentive plans
Total compensation cost	$ 689	458	$ 1,949	1,274
Stock options | General and administrative
Stock option and incentive plans
Total compensation cost	640	695	2,459	2,302
Restricted stock
Stock option and incentive plans
Total compensation cost	$ 10	18	$ 30	69
Shares
Outstanding (in shares)	32,400		32,400
Issued (in shares)			0
Vested (in shares)			52,600
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	7	$ 15	18
Restricted stock | General and administrative
Stock option and incentive plans
Total compensation cost	$ 5	$ 11	$ 15	$ 51
2005 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	0		0
2005 Plan | Stock options
Stock Options
Outstanding (in shares)	330,450		330,450
2014 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	349,753		349,753
2014 Plan | Stock options
Stock Options
Outstanding (in shares)	7,435,038		7,435,038
Granted (in shares)			3,672,000
2014 Plan | Restricted stock
Shares
Outstanding (in shares)	32,400		32,400
Equity Incentive Plan, Employee Inducments | Stock options
Stock Options
Granted (in shares)			410,000