Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2017

Summary of Assumptions Used in Black-Scholes Option Pricing Model

The fair values of stock options granted during the three and six months ended June 30, 2017 and 2016 were estimated as of the dates of grant using the Black-Scholes option pricing model with the following assumptions:

	Three Months Ended June 30,		Six Months Ended June 30,
	2017	2016	2017	2016
Risk-free interest rate	1.85% - 1.88%	1.23% - 1.79%	1.85% - 2.57%	1.23% - 1.79%
Expected volatility	83.3%	69.3% - 72.6%	75.3% - 83.3%	67.8% - 72.6%
Expected dividend yield	0%	0%	0%	0%
Expected life of employee options (in years)	6.25	6.25	6.25	6.25
Expected life of nonemployee options (in years)	10	10	10	10

Summary of Compensation Expense Relating to Stock Options

During the three and six months ended June 30, 2017 and 2016, the Company recognized compensation expense relating to stock options, as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
Research and development	$	603	$	303	$	1,166	$	492
General and administrative		715		394		1,260		702
Total stock option expense	$	1,318	$	697	$	2,426	$	1,194

Summary of Stock Option Activity

A summary of stock option award activity related to employees, non-employee members of the Company’s Board of Directors and non-employee consultants as of and for the six months ended June 30, 2017 is presented below:

	Number of Shares			Weighted Average Exercise Price
Outstanding, December 31, 2016		2,548,408		$	8.75
Granted		838,500			17.55
Exercised		(153,122	)		8.91
Forfeited		(115,000	)		7.74
Outstanding, June 30, 2017		3,118,786			11.14
Options exercisable, June 30, 2017		1,186,153		$	9.43

Re-Measurement [Member]

Summary of Assumptions Used in Black-Scholes Option Pricing Model

As of June 30, 2017 and 2016, the Company used the Black-Scholes option valuation model with the following assumptions to re-measure the fair value of all outstanding options that had been granted to non-employee consultants during the vesting period of each tranche in accordance with ASC 505-50:

	As of June 30,
	2017	2016
Risk-free interest rate	2.02% - 2.28%	1.49%
Expected volatility	76.4% - 81.3%	70.80%
Expected dividend yield	0%	0%
Expected life of non-employee options (in years)	6.58 - 9.69	7.59