Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2015

Stock-Based Compensation Expense on All Employee and Non-Employee Awards

The Company recognized stock-based compensation expense on all employee and non-employee awards as follows:

	For the three months ended September 30,				For the nine months ended September 30,
(in thousands)	2015		2014		2015		2014
Research and development	$	264	$	340	$	874	$	1,126
General and administrative		1,213		808		5,180		2,457
Stock-based employee compensation expense	$	1,477	$	1,148	$	6,054	$	3,583

Fair Value of Stock Options Assumptions Using Black-Scholes Option Valuation Model

For the three months ended September 30, 2015 and 2014, the fair value of stock options was estimated on the date of grant using a Black-Scholes option valuation model with the following assumptions:

	For the three months ended September 30,
	2015	2014
Risk-free interest rate	1.66 - 1.93%	2.03%
Expected life in years	6	6
Expected volatility	80.01 - 81.17%	92.36%
Expected dividend yield	0	0

Stock Option Activity Under Stock Option Plan

Stock option activity under the Company’s stock option plan for the nine months ended September 30, 2015 is as follows:

(in thousands, except share and per share data)	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding, December 31, 2014		6,505,663		$	4.07
Granted		254,800			11.61
Exercised		(2,938,161	)		3.96
Cancelled		(167,167	)		4.13
Outstanding, September 30, 2015		3,655,135		$	4.69		7.09	$	16,481
Vested and unvested expected to vest at September 30, 2015		3,579,108		$	4.09		5.59	$	16,139
Options exercisable, September 30, 2015		1,886,001		$	4.09		5.59	$	9,277
Options exercisable, December 31, 2014		3,781,162		$	4.10		5.80	$	4,130
Options available for future grant		3,441,950

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the nine months ended September 30, 2015 is as follows:

	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2014		144,508		$	4.70
Granted		1,054,186			9.36
Vested		(70,991	)		4.62
Cancelled		—			—
Non-vested, September 30, 2015		1,127,703		$	9.06