Stock Option and Incentive Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
2005 Stock option and incentive plans
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price			$ 6.13
Total stock based compensation expense	$ 388	$ 24	$ 771	$ 47
Research and development
2005 Stock option and incentive plans
Total stock based compensation expense	131	2	257	3
General and administrative
2005 Stock option and incentive plans
Total stock based compensation expense	$ 257	$ 22	$ 514	$ 44
Stock option
2005 Stock option and incentive plans
Stock options outstanding	1,410,712		1,410,712
Weighted average exercise price (in dollars per share)	$ 4.88		$ 4.88
Granted of stock options (in shares)			10,000
Exercise of stock options (in shares)			224,912
Exercised (in dollars per share)			$ 1.04
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period			44,950
2005 Plan
2005 Stock option and incentive plans
Common stock reserved for issuance (in shares)	0		0
Stock options outstanding	730,573		730,573
2014 Plan
2005 Stock option and incentive plans
Common stock reserved for issuance (in shares)	580,171		580,171
Stock options outstanding	680,139		680,139