Stock Compensation Plans (Tables)

9 Months Ended

Sep. 30, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

The following table summarizes stock option activity:



	Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding as of January 1, 2015	3,210,693		$	7.54
Granted	195,290		$	21.96
Exercised	(162,894	)	$	1.68
Forfeited or expired	(158,198	)	$	12.06
Outstanding as of September 30, 2015	3,084,891		$	8.53	7.34	$	1,545,386
Options vested and expected to vest as of September 30, 2015	3,038,336		$	8.41	7.31	$	1,544,310
Options exercisable as of September 30, 2015	2,787,059		$	7.17	7.12	$	1,545,386

Ranges of Underlying Assumptions Used in BSM Option Pricing Model to Determine Fair Value of Stock Options Granted to Employees and Nonemployees

The following are the ranges of underlying assumptions used in the BSM option pricing model to determine the fair value of stock options granted to employee and to non-employees:



	Nine Months Ended September 30,
	2015	2014
Employees:
Risk-free interest rate	1.76% - 1.85%	1.60% - 1.88%
Expected dividend yield	0%	0%
Expected volatility	74.1% - 92.2%	81.0% - 85.0%
Expected term of options (years)	5.9 - 6.0	6.0
Fair value of common stock	$18.87 - $26.71	$7.55 - $24.04
Non-employees:
Risk-free interest rate	0.10% - 1.56%	0.11% - 1.20%
Expected dividend yield	0%	0%
Expected volatility	56.2% - 92.6%	73.0% - 85.0%
Expected term of options (years)	0.3 - 6.0	1.0 - 4.0
Fair value of common stock	$4.04 - $25.01	$11.31 - $27.24

Schedule of Stock-based Compensation Expense Valuation Analysis Probability-Weighted Scenarios

March 31, 2014 Valuation Analysis

Our analysis considered the following probability-weighted scenarios:



Scenario	Weight
IPO by April 15, 2014	65%
Sale by September 30, 2015	10%
Private company	15%
Dissolution	10%

February 12, 2014 Valuation Analysis

Our analysis considered the following probability-weighted scenarios:



Scenario	Weight
IPO by May 15, 2014	25%
Sale by September 30, 2015	10%
Private company	50%
Dissolution	15%

Schedule of Stock-based Compensation Expense for Stock Awards Recognized

Total stock-based compensation expense for all stock awards recognized in our condensed consolidated statements of operations is as follows (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Employees:
Research and development	$	529	$	194	$	1,080	$	517
General and administrative	537		238		1,405		642
Total	$	1,066	$	432	$	2,485	$	1,159
Non-employees:
Research and development	$	31	$	211	$	372	$	572
General and administrative	46		14		86		34
Total	$	77	$	225	$	458	$	606