SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

6 Months Ended

Jun. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Summary of allocation of stock-based compensation expense included in operating expenses on condensed statements of operations related to share-based payment awards

The following table summarizes the stock-based compensation expense included in operating expenses on our condensed statements of operations related to stock options and employee stock purchases for the three and six months ended June 30, 2020 and 2019, which was allocated as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
(In thousands)	2020		2019		2020		2019
Research and development	$	579	$	413	$	1,080	$	653
General and administrative		1,128		1,021		2,195		2,207
Stock-based compensation expense included in operating expenses	$	1,707	$	1,434	$	3,275	$	2,860

Schedule of assumptions used to estimate the fair value of service-based and performance-based stock options granted

The fair value of service-based and performance-based options granted during the three and six months ended June 30, 2020 and 2019 has been estimated at the date of grant using the Black Scholes option-pricing model with the following assumptions:

	Six Months Ended June 30,
	2020	2019
Dividend yield	0%	0%
Expected volatility range	0.781 to 0.790	0.802 to 0.980
Risk-free interest rate range	0.37% to 1.62%	1.79% to 2.56%
Expected term range	5.25 yrs	5.25 yrs to 6.44 yrs

Schedule of assumptions used to estimate the fair value of employee stock purchases under the purchase plan

The fair value of employees’ purchase rights during the three and six months ended June 30, 2020 and 2019 has been estimated using the Black Scholes option-pricing model with the following assumptions:

	Six Months Ended June 30,
	2020	2019
Dividend yield	0%	0%
Expected volatility range	0.478 to 0.564	1.333 to 1.653
Risk-free interest rate range	1.56% to 1.57%	2.56% to 2.63%
Expected term range	6 mos to 12 mos	6 mos to 12 mos