Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following table summarizes stock option activity for the 2002 Plan and 2018 Plan for the year ended December 31, 2018:

				Weighted-		Weighted-
				Average		Average
				Exercise		Remaining		Aggregate
	Total			Price Per		Contractual		Intrinsic
	Options			Share		Term (in years)		Value
Outstanding at Ended December 31, 2016		1,001,546		$	1.62		8.1	$	58,619
Granted		99,866		$	1.44
Exercised		(2,547	)	$	1.20
Cancelled or expired		(23,656	)	$	1.76
Outstanding at December 31, 2017		1,075,209		$	1.60		7.3	$	711,328
Granted		563,268		$	4.07
Exercised		(43,687	)	$	2.12
Cancelled or expired		(49,387	)	$	1.65
Outstanding at December 31, 2018		1,545,403		$	2.48		7.6	$	1,593,487
Vested and expected to vest at December 31, 2018		1,545,403		$	2.48		7.6	$	1,593,487
Vested and exercisable at December 31, 2018		801,294		$	1.65		6.3	$	1,175,200

Estimated Fair Value of Option on Grant Date using Weighted Average Assumptions

The fair value of each option was estimated on the date of grant using the weighted average assumptions in the table below:

	Year Ended
	December 31,
	2018			2017
Risk-free interest rate		2.88	%		2.88	%
Expected term (in years)	7.0			7.1
Expected volatility		69	%		68	%
Expected dividend yield		—			—
Estimated fair value of common stock	$	4.07		$	1.00

Stock-based Compensation Expense

Stock-based compensation expense has been reported in the Company’s statements of operations for the years ended December 31, 2018 and 2017 as follows (in thousands):

	Year Ended
	December 31,
	2018		2017
General and administrative	$	208	$	40
Research and development		124		37
Total stock-based compensation	$	332	$	77