Stock-Based Compensation

The Company accounts for its stock-based compensation at fair value. The following table summarizes stock-based compensation expense by financial statement line item for the

three

months ended

June 30, 2020

and

2019

(in thousands):

	Three Months Ended June 30,
	2020		2019
Cost of revenues	$	28	$	3
Research and development		130		10
Selling, general and administrative		751		236
Total	$	909	$	249

The Company issued

27,341

shares of immediately vested common stock and

658,667

shares of restricted stock awards during the

three

months ended

June 30, 2020

and issued

13,174

shares of immediately vested common stock and

160,500

shares of restricted stock awards during the

three

months ended

June 30, 2019

. These restricted stock awards generally vest over

years. Awards for restricted stock include both time-based and performance-based awards. For options and restricted stock awards that vest upon the passage of time, expense is being recorded over the vesting period. Performance-based awards are expensed over the requisite service period based on probability of achievement.

The estimated fair value of the Company's stock-based awards, less expected annual forfeitures, is amortized over the awards' service period. The total unrecognized compensation cost for unvested outstanding stock options was less than $

0.1

million at

June 30, 2020

. This expense will be recognized over a weighted average expense period of approximately

0.9

years. The total unrecognized compensation cost for unvested outstanding restricted stock was $

6.3

million at

June 30, 2020

. This expense will be recognized over a weighted-average expense period of approximately

2.1

years.

The Company did

not

grant any stock options during the

three

months ended

June 30, 2020

. The Company granted

5,939

stock options during the

three

months ended

June 30, 2019

. The stock options granted during the

three

months ended

June 30, 2019

will vest over

ars. The weighted average assumptions used in the Black Scholes valuation model for stock options granted during the

three

months ended

June 30, 2019

are as follows:

	Three Months Ended June 30,
	2020		2019
Expected volatility		N/A		66.5	%
Risk-free interest rate		N/A		1.8	%
Expected life (years)		N/A		5.91
Dividend yield		N/A		None