Share-Based Compensation (Tables)

6 Months Ended

12 Months Ended

Jun. 30, 2019

Dec. 31, 2018

Schedule of share-based compensation expense

Share-based compensation expense was included in general and administrative and research and development expenses as follows in the accompanying condensed statements of comprehensive loss (in thousands):


	Three Months Ended				Six Months Ended
	June 30,				June 30,
		2019		2018		2019		2018
General and administrative	$	275	$	436	$	559	$	1,147
Research and development		163		473		352		782
Total share-based compensation	$	438	$	909	$	911	$	1,929

Share-based compensation expense was included in general and administrative and research and development costs as follows in the accompanying statements of comprehensive loss (in thousands):


	Year Ended
	December 31,
	2018		2017		2016
General and administrative	$	2,378	$	4,091	$	1,166
Research and development		1,753		1,182		552
Total share-based compensation	$	4,131	$	5,273	$	1,718

Schedule of weighted-average assumptions, option-pricing model

The weighted‑average assumptions used in the Black‑Scholes option‑pricing and Monte Carlo simulation models are as follows:


	Three Months Ended		Six Months Ended
	June 30,		June 30,
	2019	2018	2019	2018

Expected stock price volatility	—	66.0%	—	66.3%
Expected life of options (years)	—	5.7	—	5.8
Expected dividend yield	—	0%	—	0%
Risk free interest rate	—	2.9%	—	2.7%


	Year Ended
	December 31,
	2018			2017			2016

Expected stock price volatility		66.3	%		65.8	%		71.447	%
Expected life of options (years)		5.8			5.9			6.02
Expected dividend yield		0	%		0	%		0	%
Risk free interest rate		2.7	%		2.0	%		1.2	%