Stock Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Stock-Based Compensation Expense

Stock-based compensation expense

Total stock-based compensation expense for employees, directors and non-employees for the three and nine months ended September 30, 2018 and 2017 is as follows:

	Three months ended September 30,				Nine months ended September 30,
	2018		2017		2018		2017
Research and development	$	325,466	$	29,917	$	625,813	$	52,040
General and administrative		393,132		27,967		1,041,977		64,102
	$	718,598	$	57,884	$	1,667,790	$	116,142

Schedule of Stock Options Valuation Assumptions Using a Black-Scholes Option Pricing Model

The assumptions used in Black-Scholes option pricing model for the three and nine months ended September 30, 2018 and 2017 are as follows:

	Three months ended September 30,		Nine months ended September 30,
	2018	2017	2018	2017
Expected volatility	56.56% - 56.64%	54.38%	52.80% - 60.12%	53.52% - 54.38%
Weighted-average risk-free interest rate	2.77% - 3.00%	1.76%	2.33% - 3.00%	1.76% - 2.28%
Expected dividend yield	— %	— %	— %	— %
Expected term (in years)	6.25	6.25	5.5 - 7.6	6.25
Underlying common stock fair value	$15.96 - $20.41	$2.89	$6.63 - $20.98	$0.63 - $2.89

Summary of Option Activity under Plans

A summary of option activity under the Plans for the nine months ended September 30, 2018 is as follows:

	Number of Options			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding at January 1, 2018		1,971,711		$	3.61		9.3	$	5,977,162
Granted		870,059		$	16.09
Exercised		(73,296	)	$	1.50
Cancelled/Forfeited		(71,525	)	$	2.71
Outstanding at September 30, 2018		2,696,949		$	7.79		8.9	$	40,650,382
Vested and expected to vest at    September 30, 2018		2,696,949		$	7.79		8.9	$	40,650,382
Exercisable at September 30, 2018		589,913		$	3.42		8.3	$	11,470,476

Summary of Unvested Common Stock from Early Exercises Subject to Repurchase

A summary of the Company’s unvested common stock from early exercises that is subject to repurchase by the Company is as follows:

	Shares
Unvested shares - January 1, 2018		265,098
Vested		(97,250	)
Exercised		16,150
Repurchased		—
Unvested shares - September 30, 2018		183,998