Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock option
Stock option and incentive plans
Total compensation cost	$ 553	$ 752	$ 1,878	$ 2,228
Stock Options
Outstanding (in shares)	2,910,761		2,910,761
Outstanding, weighted-average exercise price (in dollars per share)	$ 4.99		$ 4.99
Granted (in shares)			829,800
Granted, weighted-average exercise price (in dollars per share)			$ 1.27
Forfeited (in shares)			158,083
Forfeited, weighted-average exercise price (in dollars per share)			$ 7.85
Stock option | Research and development
Stock option and incentive plans
Total compensation cost	$ 172	265	$ 542	710
Stock option | General and administrative
Stock option and incentive plans
Total compensation cost	381	487	1,336	1,518
Restricted stock
Stock option and incentive plans
Total compensation cost	$ 179	48	$ 373	48
Shares
Outstanding (in shares)	239,800		239,800
Issued (in shares)			245,200
Vested (in shares)			179,700
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	$ 51	19	$ 100	19
Restricted stock | General and administrative
Stock option and incentive plans
Total compensation cost	$ 128	$ 29	$ 273	$ 29
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)	1,258,825		1,258,825
2014 Plan | Stock option
Stock Options
Outstanding (in shares)	2,479,839		2,479,839
2014 Plan | Restricted stock
Shares
Outstanding (in shares)	239,800		239,800