Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2016

Stock option activity under the Company’s stock option plan was as follows:

	Options Outstanding
	Shares Available for Grant				Number of Options			Weighted- Average Exercise Price		Aggregate Intrinsic Value
										(In thousands)
Balance—December 31, 2013		92,278				4,029,331		$	0.72	$	985
Authorized		5,071,079				—
Granted		(2,019,598	)			2,019,598		$	1.00
Exercised		—				(66,499	)	$	0.74
Canceled		10,996		⁽¹⁾		(12,048	)	$	9.33
Balance—December 31, 2014		3,154,755				5,970,382		$	0.80	$	4,335
Authorized		6,494,292				—
Granted		(4,893,562	)			4,893,562		$	9.94
Exercised		—				(836,241	)	$	0.82
Canceled		54,786		⁽¹⁾		(96,474	)	$	1.74
Balance—December 31, 2015		4,810,271				9,931,229		$	5.29	$	229,591
Authorized		2,543,513				—
RSU granted, net		(657,200	)			—
Granted		(1,760,210	)			1,760,210		$	12.43
Exercised		—				(873,735	)	$	1.03
Canceled		75,085		⁽¹⁾		(127,548	)	$	18.87
Balance—December 31, 2016		5,011,459				10,690,156		$	6.65	$	74,984
Options exercisable—December 31, 2016						5,688,319		$	3.95	$	50,871
Options vested and expected to vest—December 31, 2016						10,440,713		$	6.54	$	74,087

⁽¹⁾	The amount excludes 52,463, 41,688 and 1,052 canceled options for the years ended December 31, 2016, 2015 and 2014, respectively, initially granted from the legacy stock option plans. As these plans have been terminated, any options canceled are not added back to the existing option plan pool.

Summary of Restricted Stock Unit Activity

The following table summarizes restricted stock unit activity:

	RSUs Outstanding
	Number of Restricted Stock Units			Weighted- Average Grant Date Fair Value Per Share

Balance—December 31, 2015		—		$	—
Granted		662,800			14.29
Vested		—			—
Canceled/forfeited		(5,600	)		14.29
Balance—December 31, 2016		657,200		$	14.29

Summary of Stock-Based Compensation

Total stock-based compensation expense recognized was as follows (in thousands):

	Year Ended December 31,
	2016		2015		2014

Research and development	$	9,131	$	2,493	$	202
General and administrative		5,875		5,937		368
Total stock-based compensation expense	$	15,006	$	8,430	$	570

2015 ESPP

Schedule of Black-Scholes Option-Pricing Model

The following table summarizes the assumptions used in the Black-Scholes option-pricing model to determine fair value of the Company’s common shares to be issued under the ESPP:

	Year Ended December 31,
	2016	2015
Expected term (in years)	0.5	0.5
Volatility	73.83 - 74.39%	71.70 - 72.22%
Risk-free interest rate	0.38 - 0.62%	0.08 - 0.33%
Dividend yield	—%	—%

Employees

Schedule of Black-Scholes Option-Pricing Model

The fair value of stock option awards granted to employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:

	Year Ended December 31,
	2016	2015	2014
Expected term (in years)	5.3 - 6.1	5.3 – 6.1	5.3 – 6.1
Volatility	72.3 - 74.5%	70.2 – 82.3%	70.2 – 77.3%
Risk-free interest rate	1.25 - 2.07 %	1.46 – 1.92%	1.85 – 2.0%
Dividend yield	—%	—%	—%

Non Employees

Schedule of Black-Scholes Option-Pricing Model

The fair value of stock option awards granted to non-employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:

	Years Ended December 31,
	2016	2015	2014
Expected term (in years)	6.0 - 9.6	9.1 – 9.9	9.3 – 9.7
Volatility	72.8 - 74.3%	72.1 – 83.8%	78.0 – 78.1%
Risk-free interest rate	1.35 - 2.48 %	2.06 – 2.36%	2.19 – 2.39%
Dividend yield	—%	—%	—%