Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock option
Stock option and incentive plans
Total compensation cost	$ 664	$ 738	$ 1,325	$ 1,476
Stock Options
Outstanding (in shares)	2,908,836		2,908,836
Outstanding, weighted-average exercise price (in dollars per share)	$ 4.98		$ 4.98
Granted (in shares)			818,800
Granted, weighted-average exercise price (in dollars per share)			$ 1.82
Forfeited (in shares)			149,008
Forfeited, weighted-average exercise price (in dollars per share)			$ 8.26
Stock option | Research and development
Stock option and incentive plans
Total compensation cost	$ 175	213	$ 370	446
Stock option | General and administrative
Stock option and incentive plans
Total compensation cost	489	$ 525	955	$ 1,030
Restricted stock
Stock option and incentive plans
Total compensation cost	$ 108		$ 194
Shares
Outstanding (in shares)	409,300		409,300
Issued (in shares)			245,200
Vested (in shares)			7,800
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	$ 31		$ 49
Restricted stock | General and administrative
Stock option and incentive plans
Total compensation cost	$ 77		$ 145
2005 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	0		0
2005 Plan | Stock option
Stock Options
Outstanding (in shares)	430,922		430,922
2014 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	1,259,850		1,259,850
2014 Plan | Stock option
Stock Options
Outstanding (in shares)	2,477,914		2,477,914
2014 Plan | Restricted stock
Shares
Outstanding (in shares)	409,300		409,300