Share/Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Employee and Nonemployee Stock Option Activity

The following table summarizes employee and nonemployee stock option activity for the year ended December 31, 2017:

	Shares Issuable Under Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)		(in thousands)
Outstanding as of December 31, 2016		1,146,935		$	5.64		8.64	$	440
Granted		1,971,300			5.22
Exercised		(200,600	)		3.50
Forfeited		(556,275	)		6.76
Outstanding as of December 31, 2017		2,361,360		$	5.21		8.72	$	2,482
Options vested and expected to vest as of December 31, 2017		2,351,832		$	5.22		8.72	$	2,464
Options exercisable as of December 31, 2017		565,920		$	6.47		6.80	$	318

Summary of Employee and Non-Employee Restricted Stock Activity

The following table summarizes employee and nonemployee restricted stock activity for the year ended December 31, 2017:

	Shares			Weighted Average Grant Date Fair Value
Unvested restricted common stock as of December 31, 2016		75,932		$	1.96
Granted		—			—
Vested		(42,206	)		1.86
Forfeited		(419	)		1.72
Unvested restricted common stock as of December 31, 2017		33,307		$	1.84

Summary of Share/Stock-Based Compensation Expense

Total share/stock-based compensation expense recognized from the Company’s equity incentive plans and the 2016 ESPP for the years ended December 31, 2017, 2016, and 2015 was as follows (in thousands):

	Year Ended December 31,
	2017				2016				2015
	Employees		Non-Employees		Employees		Non-Employees		Employees		Non-Employees
Research and development	$	961	$	—	$	389	$	—	$	101	$	340
General and administrative		1,531		—		832		—		326		—
Total share/stock-based compensation expense	$	2,492	$	—	$	1,221	$	—	$	427	$	340

Summary of Weighted-Average Assumptions Used in Calculating Fair Value of Awards

The following table summarizes the weighted-average assumptions used in calculating the fair value of the awards:

	Year Ended December 31,
	2017			2016			2015
2016 Plan and 2015 Plan
Expected term		5.88			5.99			6.29
Expected volatility		86	%		87	%		87	%
Risk-free interest		2.00	%		1.28	%		1.37	%
Dividend yield		0	%		0	%		0	%
2016 ESPP
Expected term		0.50			0.45			—
Expected volatility		78	%		82	%		—
Risk-free interest		1.06	%		0.50	%		—
Dividend yield		0	%		0	%		—