Stock-Based Payments (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of status of stock options and changes during the period

A summary of the status of stock options as of December 31, 2019 and December 31, 2018 and changes during the year ended December 31, 2019 is presented below:

								Aggregate
				Weighted		Remaining		Intrinsic
				Average		Contractual		Value
	Shares			Exercise Price		Life (in years)		(in thousands)
Outstanding at December 31, 2018		3,732,643		$	9.88	7.9		$	1,694
Granted		1,175,500			6.68
Exercised		(60,181	)		3.48
Cancelled		(229,541	)		9.55
Outstanding at December 31, 2019		4,618,421		$	9.16		7.5	$	2,525
Exercisable at December 31, 2019		2,407,267		$	9.41		6.6	$	2,190

Summary of status of restricted stock units and changes during the period

A summary of the status of restricted stock units as of December 31, 2018 and December 31, 2019 and changes during the year ended December 31, 2019 is presented below:

				Weighted
				Average Grant
	Shares			Date Fair Value
Outstanding at December 31, 2018		—		$	—
Granted		1,168,424			6.75
Vested		—			—
Forfeited		(52,066	)		6.71
Outstanding at December 31, 2019		1,116,358		$	6.75

Schedule of weighted-average assumptions used in Black-Scholes option-pricing model

The fair value of each stock option granted was estimated on the date of grant using the Black-Scholes option-pricing model based on the following weighted-average assumptions:

	Year Ended December 31,
	2019			2018			2017
Weighted-average risk-free interest rate		2.42	%		2.56	%		2.07	%
Expected dividend yield		—	%		—	%		—	%
Expected option term (in years)		6.00			6.04			6.05
Volatility		91.35	%		90.26	%		87.83	%

Summary of stock-based compensation expense for stock options granted to employee and non-employees and from employee stock purchase plan

The following table summarizes the stock-based compensation expense for stock options, restricted stock units and restricted common stock granted to employees and non-employees and from the 2016 ESPP recorded in the Company’s statements of operations:

	Year Ended December 31,
	2019		2018		2017
Research and development	$	3,472	$	2,412	$	1,666
General and administrative		6,367		4,198		2,753
Total stock-based compensation expense	$	9,839	$	6,610	$	4,419