Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2019

Equity [Abstract]

Summary of Option Activity under 2018 Plan, 2013 Plan and 2010 Plan

A summary of option activity under the 2018 Plan, 2013 Plan, and 2010 Plan for the six months ended June 30, 2019, is as follows:

Year-to-Date Activity	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in millions)
Options outstanding at December 31, 2018		781,725		$	16.34		9.0
Granted		563,150			23.10
Exercised		(7,813	)		11.81
Cancelled/forfeited		(353,556	)		23.51
Options outstanding at June 30, 2019		983,506			17.42		8.0	$	0.1
Options exercisable at June 30, 2019		314,635		$	11.62		7.2	$	0.1

Summary of Restricted Stock Unit Activity under 2018 Plan

A summary of restricted stock unit activity under the 2018 Plan for the six months ended June 30, 2019, is as follows:

Year-to-Date Activity	Number of Shares		Weighted Average Grant Date Fair Value Per Share		Aggregate Intrinsic Value (in millions)
Non-vested outstanding at December 31, 2018		—		—
Granted		15,000	$	23.60
Non-vested outstanding at June 30, 2019		15,000	$	23.60	$	0.1

Summary of Stock-Based Compensation Expense

The amount of stock-based compensation expense recorded to research and development and to general and administrative is detailed in table below:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Stock-based compensation
Research and development	$	317,148	$	182,919	$	619,134	$	335,654
General and administrative		398,218		143,508		768,159		243,148
	$	715,366	$	326,427	$	1,387,293	$	578,802