Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Stock option
Stock option and incentive plans
Total compensation cost	$ 661	$ 739
Stock Options
Outstanding (in shares)	2,648,836
Outstanding, weighted-average exercise price (in dollars per share)	$ 5.34
Granted (in shares)	558,800
Granted, weighted-average exercise price (in dollars per share)	$ 1.21
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	$ 195	233
Stock option | General and administrative
Stock option and incentive plans
Total compensation cost	466	$ 506
Restricted stock
Stock option and incentive plans
Total compensation cost	$ 86
Shares
Issued (in shares)	245,200
Vested (in shares)	0
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	$ 18
Restricted stock | General and administrative
Stock option and incentive plans
Total compensation cost	$ 68
2005 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	0
2005 Plan | Stock option
Stock Options
Outstanding (in shares)	430,922
2014 Plan
Stock option and incentive plans
Common stock reserved for issuance (in shares)	185,835
2014 Plan | Stock option
Stock Options
Outstanding (in shares)	2,217,914
2014 Plan | Restricted stock
Shares
Outstanding (in shares)	420,400