The amount of share-based compensation expense recognized by the Company by location in its statements of operations for the years ended December 31, 2020, 2019, and 2018 is as follows (in thousands):

	Years ended December 31,
	2020		2019		2018
Cost of revenues	$	66	$	67	$	21
Sales and marketing		1,813		1,339		926
General and administrative		2,076		1,596		646
Research and development		449		432		150
Total	$	4,404	$	3,434	$	1,743

In June 2018, the Company adopted the 2018 Equity Incentive Plan, or 2018 Plan, which authorized the issuance of up to 1.4 million shares in the form of restricted stock, stock appreciation rights and stock options to the Company’s directors, employees and consultants. The amount and terms of grants are determined by the Company’s board of directors. All stock options granted to date have had exercise prices equal to the fair value, as determined by the closing price as reported by the Nasdaq Global Market on the date of grant, of the underlying common stock on the date of grant. The contractual term of stock options is up to 10 years, and stock options are exercisable in cash or as otherwise determined by the board of directors. Generally, stock options vest 25% upon the first anniversary of the date of grant and the remainder ratably monthly thereafter for 36 months. Restricted stock awards and restricted stock units generally vest ratably in three equal installments on the first, second and third anniversaries of the grant date. As of December 31, 2020, there were 1.5 million shares available for future issuance under the 2018 Plan.

In December 2020, the Company adopted the 2020 Inducement Incentive Plan, which authorized the issuance of up to 400,000 shares in the form of stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance stock awards and other stock awards to eligible employees who satisfy the standards for inducement grants under Nasdaq global market rules. An individual who previously served as an employee or director of the Company is not eligible to receive awards under this plan. The amount and terms of grants are determined by the Company’s board of directors. As of December 31, 2020, there were 400,000 shares available for future issuance under the 2020 Inducement Incentive Plan.

The following table summarizes the Company’s stock option activity for the years ended December 31, 2020, 2019 and 2018:

	Number of Shares under Option (in thousands)			Weighted- average Exercise Price per Option		Weighted- average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2017		2,444		$	2.39
Granted		584			8.33
Exercised		(194	)		2.60
Forfeited		(123	)		3.73
Outstanding at December 31, 2018		2,711			3.59
Granted		856			14.27
Exercised		(879	)		2.82
Forfeited		(273	)		8.33
Outstanding at December 31, 2019		2,415			7.11
Granted		1,028			2.01
Exercised		(371	)		1.86
Forfeited		(707	)		10.76
Outstanding at December 31, 2020		2,365		$	4.62		6.75		16,779
Exercisable at December 31, 2020		1,071		$	5.31		3.75		7,027
Vested and expected to vest at December 31, 2020		2,365		$	4.62		6.75		16,779

The Company recognized share-based compensation expense related to stock options of $1.7 million, $2.2 million, $1.6 million for the years ended December 31, 2020, 2019, and 2018, respectively. As of December 31, 2020, there was $2.7 million of total unrecognized compensation cost related to non-vested stock options which the Company expects to recognize over a weighted-average period of 2.7 years. The weighted-average grant-date fair value of stock options granted during the years ended December 31, 2020, 2019, and 2018 was estimated at $1.09, $7.69, and $5.03 per option. The total intrinsic value of stock options exercised during the years ended December 31, 2020, 2019, and 2018 was $1.4 million, $10.8 million, and $3.3 million, respectively.

For the years ended December 31, 2020, 2019, and 2018, the grant-date fair value of stock options was estimated at the time of grant using the following weighted-average inputs and assumptions in the Black-Scholes option pricing model:

	2020			2019			2018
Estimated fair value of common stock	$	2.01		$	14.27		$	8.41
Exercise price	$	2.01		$	14.27		$	8.41
Expected term (in years)		6.1			6.0			6.0
Risk-free interest rate		0.4	%		2.2	%		2.7	%
Expected volatility		59.5	%		55.3	%		65.3	%
Dividend yield		0	%		0	%		0	%

The following table summarizes the Company’s restricted stock award and restricted stock unit activity for the years ended December 31, 2020, 2019, and 2018:

	Non-vested Restricted Stock Awards (in thousands)			Weighted- average Grant-date Fair Value		Non-vested Restricted Stock Units (in thousands)			Weighted- average Grant-date Fair Value
Non-vested at December 31, 2017		16		$	2.32		-		$	-
Granted		-			-		43			25.21
Vested		(12	)		2.32		-			-
Non-vested at December 31, 2018		4			2.32		43			25.21
Granted		-			-		247			13.89
Vested		(4	)		2.32		(22	)		18.69
Forfeited		-			-		(23	)		15.57
Non-vested at December 31, 2019		-			-		245			15.23
Granted		-			-		2,307			3.18
Vested		-			-		(98	)		13.24
Forfeited		-			-		(594	)		5.24
Non-vested at December 31, 2020		-		$	-		1,860		$	3.58

The Company recognized share-based compensation expense related to restricted stock awards and restricted stock units of $2.7 million, $1.2 million, and $0.2 million during the years ended December 31, 2020, 2019, and 2018, respectively. As of December 31, 2020, there was $5.3 million of unrecognized compensation cost related to non-vested restricted stock units which the Company expects to recognize over a weighted-average period of 2.4 years. The total fair value at the vesting date of restricted stock awards and restricted stock units vested during the years ended December 31, 2020, 2019, and 2018 was $0.3 million, $0.3 million, and $0.2 million, respectively.

In July 2020, the Company awarded 500,000 performance restricted stock units (“PRSUs”) to the Company’s chief executive officer in connection with the commencement of his employment. The grant was comprised of four equal tranches each of which vest in equal installments of 125,000 shares based on appreciation of the Company’s common stock price to $10, $15, $20 and $25 per share, respectively, measured using a trailing 30-day volume weighted average price of a share of the Company’s common stock. The fair value of the PRSUs was determined based upon a risk neutral Monte Carlo simulation valuation model. The Company’s assumptions for expected volatility, closing price and risk-free rate were 87.4%, $1.98 and 0.63%, respectively. The aggregate estimated fair value of the PRSUs was $0.9 million, which is expected to be recognized over a weighted-average period of 3.9 years. The Company recognized $0.1 million in share-based expense related to the PRSU award for the year ended December 31, 2020. As of December 31, 2020, there was $0.8 million of unrecognized compensation costs which the Company plans to recognize over the weighted average period of 3.4 years.