Share-Based Payments (Tables)

9 Months Ended

Sep. 30, 2015

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

Summary of Stock Option Activity and Related Information

A summary of the Company’s stock option activity and related information follows:

	Shares		Weighted-Average Exercise Price		Remaining Contractual Life (in years)
Outstanding at December 31, 2014	1,438,528		$	4.93	7.86
Granted	799,828		8.69
Exercised	(75,549	)	0.77
Cancelled or forfeited	(230,318	)	8.79
Outstanding at September 30, 2015	1,932,489		$	6.19	7.91
Exercisable at September 30, 2015	828,209		$	4.96	7.28
Vested and expected to vest at September 30, 2015(1)	1,637,621		$	6.67	8.13

(1) Represents the number of vested options, plus the number of unvested options expected to vest.

Summary of Status and Changes of Unvested Restricted Stock

A summary of the unvested restricted stock is presented below:

	Restricted Stock		Weighted-Average Grant Date Fair Value
Unvested at December 31, 2014	125,027		$	5.39
Granted	6,660		4.03
Vested	(82,920	)	2.21
Unvested at September 30, 2015	48,767		$	10.61

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

From time to time, upon approval by the Board of Directors, certain employees have been granted restricted stock units. A summary of the restricted stock units is presented below:

	Restricted Stock Units	Weighted-Average Grant Date Fair Value
Unvested at December 31, 2014	—	$	—
Granted	221,400	2.82
Vested	—	—
Unvested at September 30, 2015	221,400	$	2.82

Estimation of Fair Value of Stock Option Granted using Black-Scholes Option-Pricing Model Assumptions

The fair value of each stock option granted to employees and directors was estimated on the date of grant using the Black-Scholes option-pricing model based on the assumptions noted in the following table:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2015	2014	2015	2014
Risk-free interest rate	1.69–1.92%	1.89-2.02%	1.42–1.92%	1.80-2.02%
Expected dividend yield	—	—	—	—
Expected term (in years)	6	5.75-6	5.75-6	5.75-6
Expected volatility	69.06–69.84%	68.76-69.07%	69.06–74.11%	68.76-69.58%

Summary of Stock-based Compensation Expense

During the three and nine months ended September 30, 2015 and 2014, the Company recorded stock-based compensation expense for employee and non-employee stock options, restricted stock, and restricted stock units which was allocated as follows in the statements of operations (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Research and development expense	$	272	$	449	$	770	$	948
General and administrative expense	357		359		1,125		997
	$	629	$	808	$	1,895	$	1,945