8. Equity-Based Compensation

The Company recorded equity-based compensation expense related to all equity-based awards for employees and nonemployees, which was allocated as follows in the consolidated statements of operations (in thousands):


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Research and development expense	$	453	$	145	$	1,240	$	370
General and administrative expense		1,033		56		1,817		319
	$	1,486	$	201	$	3,057	$	689

Equity-based compensation during the three and nine months ended September 30, 2018 includes $0.3 million related to modifications of equity awards in connection with the intended retirement of the Company’s Chief Operating Officer and Head, Corporate Development, effective December 31, 2018.

Restricted Stock

The following table summarizes restricted common stock activity as of September 30, 2018:


		Weighted
		Average Fair
		Value per Share
	Number of Shares	at Issuance
Restricted common stock as of December 31, 2017	1,220,085	$	5.77
Granted	—	$
Vested	(353,549)	$	5.77
Forfeited	(3,219)	$	5.77
Restricted common stock as of September 30, 2018	863,317	$	5.77

As of September 30, 2018, the Company had unrecognized equity-based compensation expense of $4.0 million related to restricted stock issued to employees and directors, which is expected to be recognized over a period of 1.7 years.

Stock Options

The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2018:


		Weighted		Weighted
	Number of	Average Exercise		Average Remaining	Aggregate Intrinsic
	Shares	Price		Contractual Term	Value
				(in years)	(in thousands)
Outstanding as of December 31, 2017	—	$	—	—	$	—
Granted	1,509,705		9.64	—		—
Exercised	(449)		5.77	—		—
Forfeited	(8,525)		7.73	—		—
Outstanding as of September 30, 2018	1,500,731	$	9.65	9.52	$	24,157
Options exercisable as of September 30, 2018	119,066	$	8.73	9.47	$	2,017

Using the Black-Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the nine months ended September 30, 2018 was $6.81.

The following assumptions were used in determining the fair value of options granted to employees and non-employees:


	Nine Months Ended September 30, 2018
	Employees		Non-Employees
Risk-free interest rate	2.76	%	3.05	%
Expected dividend yield	—	%	-	%
Expected term (years to liquidity)	6.12		9.39
Expected volatility	81.58	%	76.80	%

As of September 30, 2018, the Company has unrecognized equity-based compensation expense related to its employee stock options of $9.0 million which the Company expects to recognize over the remaining weighted average vesting period of 3.4 years.