Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of weighted-average assumptions estimated at the date of grant using the Black-Scholes option pricing model

	2017				2016				2015
Expected stock price volatility	74.45	-	83.29	%	74.69	-	87.67	%	73.64	-	81.21	%
Expected term of options	5.3	-	6.1	years	5.2	-	6.1	years	5.2	-	6.1	years
Risk‑free interest rate	1.78	-	2.18	%	1.07	-	1.86	%	1.44	-	1.92	%
Expected annual dividend yield			0	%			0	%			0	%

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

That expense is expected to be recognized over the next four years as follows, in thousands:

2018	$	3,164
2019		1,616
2020		1,275
2021		45
	$	6,100

Stock options

Schedule of total compensation cost recognized in the statement of operations

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

	Year Ended
	Year Ended December 31,
	2017		2016		2015
Research and development	$	724	$	980	$	685
General and administrative		1,697		1,975		1,423
Total	$	2,421	$	2,955	$	2,108

Summary of activity for all options

A summary of activity for the years ended December 31, 2017, 2016 and 2015 is presented below (in thousands, except share and per share amounts):

		Weighted‑
		Average		Aggregate
		Exercise Price		Intrinsic
	Shares	Per Share		Value
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
Granted	603,975		2.42
Exercised	(118,365)		1.04
Forfeited	(45,792)		12.08
Outstanding—December 31, 2016	2,239,044		6.57
Granted	1,884,800		4.02
Exercised	(98,402)		1.46
Forfeited	(141,358)		7.09
Expired	(129,764)		11.75
Outstanding—December 31, 2017	3,754,320	$	5.22	$	13,529
Exercisable—December 31, 2017	1,651,896	$	6.48	$	5,128
Exercisable and expected to vest—December 31, 2017	3,754,320	$	5.22	$	13,529

Restricted stock

Schedule of total compensation cost recognized in the statement of operations

Total compensation cost recognized for all restricted stock awards in the statements of operations for the year ended December 31, 2017 is as follows (in thousands):

	Year Ended
	December 31,
	2017		2016
Research and development	$	125	$	48
General and administrative		334		74
Total	$	459	$	122

Summary of activity for all restricted stock

A summary of activity for the year ended December 31, 2017 is presented below (in thousands, except share and per share amounts):

		Weighted‑average
		Grant Date
	Shares	Fair Value per Share
Outstanding—December 31, 2015	—	$	—
Granted	196,275		1.51
Forfeited	(375)		1.50
Outstanding—December 31, 2016	195,900	$	1.51
Granted	245,200		1.26
Vested	(179,700)		1.12
Forfeited	(21,600)		0.17
Outstanding—December 31, 2017	239,800	$	1.21
Expected to vest—December 31, 2017	239,800	$	1.21