Stock Option and Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2015

Stock Option and Incentive Plans

Schedule of total compensation cost recognized for all stock option awards in the statements of operations

Total compensation cost recognized for all stock option awards in the statements of operations is as follows (in thousands):

	Year Ended
	December 31,
	2015		2014
Research and development	$	685	$	137
General and administrative		1,423		561
Total stock-based compensation expense	$	2,108	$	698

Summary of activity for all option

A summary of activity for the years ended December 31, 2015 and 2014 is presented below (in thousands, except share and per share amounts):

		Weighted‑
		Average		Aggregate
		Exercise Price		Intrinsic
	Shares	Per Share		Value
Outstanding—December 31, 2013	1,093,208	$	1.04
Granted	700,000		8.99
Exercised	(122,634)		1.04
Outstanding—December 31, 2014	1,670,574		4.37
Granted	585,800		12.56
Exercised	(327,098)		1.14
Forfeited	(44,950)		6.13
Expired	(85,100)		1.04
Outstanding—December 31, 2015	1,799,226	$	7.74	$	3,786
Exercisable—December 31, 2015	785,174	$	5.05	$	2,834
Exercisable and expected to vest—December 31, 2015	1,799,226	$	7.74	$	3,786

Schedule of weighted-average assumptions estimated at the date of grant using the Black-Scholes option pricing model for weighted-average grant date fair value of the options granted to employees

	2015				2014
Expected stock price volatility	73.64	-	81.21	%	77.66	-	86.08	%
Expected term of options	5.2	-	6.1	years	5.5	-	6.06	years
Risk‑free interest rate	1.44	-	1.92	%	1.75	-	1.98	%
Expected annual dividend yield			0	%			0	%

Schedule of unrecognized compensation expense expected to be recognized in future years

That expense is expected to be recognized in the years ended as follows, in thousands:

2016	$	2,863
2017		2,256
2018		1,293
2019		146
	$	6,558