Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Schedule of weighted-average assumptions used to estimate grant date fair value of stock options

The weighted-average assumptions used to estimate grant date fair value of stock options using the Black-Scholes option pricing model were as follows for the years ended December 31, 2019, 2018 and 2017:



	Years ended December 31,
	2019	2018	2017
Expected common stock price volatility	110%	85%	81%
Risk-free interest rate	1.38-2.54	2.39% - 2.95%	1.82% - 2.38%
Expected term of options (years)	4.8	6.0	6.1
Expected dividend yield	—	—	—

Schedule of share-based compensation expense

Share-based compensation expense includes expenses related to stock options and RSUs granted to employees, non-employee directors and consultants, as well as the option granted to employees to purchase shares under the ESPP, all of which have been reported in the Company’s Statements of Operations as follows:



	Years ended December 31,
	2019		2018		2017
Research and development	$	4,260	$	4,967	$	11,114
General and administrative	4,920		6,105		7,057
Total	$	9,180	$	11,072	$	18,171