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Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

Stock-Based Compensation

Schedule of total employee, director and non-employee stock-based compensation expense recognized

		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2018			2017			2018			2017
General and administrative		$	2,732		$	1,422		$	6,037		$	4,305
Research and development			3,388			2,183			9,436			5,906
		$	6,120		$	3,605		$	15,473		$	10,211
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2018			2017			2018			2017
Stock options		$	5,832		$	3,462		$	14,723		$	9,820
ESPP			209			143			562			391
Restricted stock units			79			—			188			—
		$	6,120		$	3,605		$	15,473		$	10,211

Summary of stock option activity

				Weighted			Weighted
				Average			Average
		Number of		Exercise			Remaining			Aggregate
		Shares subject		Price			Contractual			Intrinsic
		to outstanding		(Per			Term			Value
		options		Share)			(in years)			(in thousands)
Balances at December 31, 2017		5,093,442		$	15.32			7.62
Options granted		1,679,400		$	26.63
Options forfeited		(107,720)		$	21.66
Options exercised		(788,409)		$	8.96
Balance at September 30, 2018		5,876,713		$	19.29			7.70		$	115,992
Exercisable		2,857,873		$	14.76			6.56		$	69,180

Schedule of weighted average assumptions used for estimation of fair value of stock options

		Options				Options
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2018		2017		2018		2017
Expected term (years)		6.1		6.1		6.1		6.1
Expected volatility		72.8	%	96.7	%	73.1	%	89.8	%
Risk-free interest rate		2.87	%	1.95	%	2.56	%	2.03	%
Expected dividend yield		—	%	—	%	—	%	—	%

Schedule of weighted average assumptions used for estimation of fair value of ESPP

		ESPP				ESPP
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
		2018		2017		2018		2017
Expected term (years)		0.5 - 2.0		0.5 - 2.0		0.5 - 2.0		0.5 - 2.0
Expected volatility		61.2 - 71.4	%	67.8 - 79.8	%	61.2 - 71.4	%	67.8 - 79.8	%
Risk-free interest rate		1.47 - 2.41	%	.47 - 1.09	%	1.47 - 2.41	%	.47 - 1.09	%
Expected dividend yield		—	%	—	%	—	%	—	%

Summary of restricted stock unity activity

				Weighted
		Restricted		Average Grant
		Stock		Date Fair Value
		Units		(Per unit)
Unvested at December 31, 2017		—		$	—
Granted		33,933		$	27.64
Vested		—		$	—
Forfeited		—		$	—
Unvested at September 30, 2018		33,933		$	27.64

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Tabular disclosure of the changes in outstanding nonvested restricted stock shares.

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Tabular disclosure of the significant assumptions used during the year to estimate the fair value of employee stock purchase plans, including, but not limited to: (a) expected term, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.

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Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.

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