Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

A summary of the Company’s stock option activity related to employees, non-employee members of the Board of Directors and non-employee consultants as of December 31, 2015 and changes during the year then ended is as follows:


	Number of Options			Weighted- Average Exercise Price		Aggregate Intrinsic Value
Outstanding at December 31, 2014		1,022,360		$	8.16
Granted		774,000			11.77
Exercised		(124,868	)		2.89
Expired		(8,000	)		0.25
Forfeited		(5,084	)		10.45
Outstanding at December 31, 2015		1,658,408		$	10.27	$	11,058
Weighted average remaining contractual life as of December 31, 2015 (yrs)		8.31
		510,298		$	7.78	$	4,634
Weighted average remaining contractual life as of December 31, 2015 (yrs)		6.59
Options vested and expected to vest at December 31, 2015		1,574,746		$	10.14	$	10,693

Weighted average remaining contractual life as of December 31, 2015 (yrs)		8.26

Summary of Assumptions Used in Black-Scholes Option Pricing Model

The fair values of the stock options granted to those groups were estimated using the Black-Scholes option valuation model with the following ranges of assumptions (see Note 2, Summary of Significant Accounting Policies - Stock-Based Compensation):


	Year Ended December 31,
	2015	2014
Risk-free interest rate	1.43% - 1.89%	1.64% - 2.72%
Expected volatility	64.0% - 67.4%	64.9% - 71.3%
Expected dividend yield	0%	0%
Expected life of employee and Board of Directors’ options (in years)	6.25	6.25
Expected life of non-employee options (in years)	10	10

Summary of Compensation Expense Relating to Stock Options

During the years ended December 31, 2015, 2014 and 2013, the Company recognized compensation expense in the accompanying Statements of Comprehensive Loss relating to stock options, as follows:


	Year Ended December 31,
	2015		2014		2013
Research and development	$	1,073	$	349	$	71
General and administrative		1,441		1,022		52

Total stock option expense	$	2,514	$	1,371	$	123

Re-Measurement [Member]

Summary of Assumptions Used in Black-Scholes Option Pricing Model

At the end of each fiscal quarter during the years ended December 31, 2015, 2014 and 2013, the Company used the Black-Scholes option valuation model with the following ranges of assumptions to re-measure the fair value of all outstanding unvested options that had been granted to non-employee consultants until each option grant was fully vested.


	Year Ended December 31,
	2015	2014	2013
Risk-free interest rate	1.81% - 2.15%	1.96% - 2.72%	2.5% - 3.2%
Expected volatility	70.6% - 72.2%	69% - 71%	71% - 72%
Expected dividend yield	0%	0%	0%
Expected life of non-employee options (in years)	8.1 - 8.8	6 - 10	1.5 – 7