Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity Under Plans

The following summarizes option activity under the 2012 Plan and 2015 Plan:

	Shares Available for Grant			Shares Subject to Outstanding Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (inthousands)
Balance at December 31, 2014		312,911			554,669		$	0.43		9.2	$	109
Options authorized		2,595,138			—			—
Options retired		(348,150	)		—			—
Options granted		(1,124,406	)		1,124,406		$	2.80
Options exercised		—			(352,978	)	$	1.00
Options repurchased		54,128			—		$	0.36
Options canceled		7,450			(7,450	)	$	0.72
Balance at December 31, 2015		1,497,071			1,318,647		$	2.29		9.0	$	16,305
Options granted		(1,069,534	)		1,069,534		$	11.57
Options exercised		—			(18,913	)	$	0.71
Options repurchased		65,984			—		$	0.74
Options canceled		227,400			(227,400	)	$	7.16
Balance at December 31, 2016		720,921			2,141,868		$	6.42		8.4	$	14,963
Options outstanding and exercisable as of    December 31, 2016					623,901		$	3.28		7.5	$	6,058
Options vested and expected to vest as of    December 31, 2016					1,898,243		$	6.61		8.4	$	12,886

Summary of Stock Options Outstanding and Currently Exercisable

The following table summarizes information with respect to stock options outstanding and currently exercisable as of December 31, 2016:

	Options Outstanding				Options Outstanding and Exercisable
Exercise Price	Number Outstanding		Weighted Average Remaining Contractual Life (in Years)		Number Exercisable		Weighted Average Exercise Price Per Share
$0.18 - $0.62		374,597		6.7		276,598	$	0.29
$1.51 - $1.51		654,861		8.2		172,886		1.51
$4.04 - $9.08		450,121		8.6		94,969		8.17
$10.00 - $15.73		443,789		9.3		79,448		11.67
$15.95 - $21.31		218,500		9.9		—		—
		2,141,868		8.4		623,901	$	3.28

Schedule of Stock-Based Compensation Expense, Net of Estimated Forfeitures

Stock-based compensation expense, net of estimated forfeitures, is reflected in the statements of operations and comprehensive income (loss) as follows (in thousands):

	Year Ended December 31,
	2016		2015		2014
Research and development	$	1,252	$	206	$	38
General and administrative		1,561		310		54
Total stock-based compensation	$	2,813	$	516	$	92

Schedule of Assumptions for Black-Scholes Option-Pricing Model Used in Determining Fair Value of Time-Based and Performance-Based Options Granted to Employees

The following table illustrates the assumptions for the Black-Scholes option-pricing model used in determining the fair value of time-based and performance-based options granted to employees:

	Year Ended December 31,
	2016		2015		2014
Risk-free interest rate	1.05%-2.10%		1.53%-1.94%		1.7%–2.0%
Expected life (in years)	5.3-6.1		5.5-6.5		6.0–6.1
Volatility	71%-73%		79%-109%		84%–94%
Dividend yield		0%		0%		0%