Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2015

Stock-Based Compensation

Summary of stock option activity

	Shares		Weighted average exercise price per share
Outstanding at January 1, 2015	8,829,343		$	6.17
Options granted	1,693,686		2.39
Options exercised	—		—
Options cancelled	(399,825	)	9.14
Outstanding at March 31, 2015	10,123,204		$	5.42
Exercisable at March 31, 2015	5,305,790		$	6.45

Summary of unvested restricted share activity

	Shares		Weighted average grant date fair value per share
Outstanding at January 1, 2015	744,514		$	3.65
Vested	(9,756	)	4.10
Granted	—		—
Forfeited	—		—
Outstanding at March 31, 2015	734,758		$	3.65

Schedule of weighted average assumptions used to estimate fair value of each employee stock option award

	Three Months Ended March 31,
	2015		2014
Risk-free interest rate	1.77	%	1.84	%
Expected life in years	6.25		6.25
Volatility	101	%	104	%
Expected dividend yield	—		—

Schedule of stock-based compensation expense

	Three Months Ended March 31,
	2015		2014
Stock-based compensation expense by type of award:
Employee stock options	$	1,508	$	2,529
Restricted stock	202		57
Total stock-based compensation expense	$	1,710	$	2,586
Effect of stock-based compensation expense by line item:
Research and development	$	981	$	1,131
General and administrative	729		1,455
Total stock-based compensation expense included in net loss	$	1,710	$	2,586

Schedule of unrecognized stock-based compensation expense

Unrecognized stock-based compensation expense as of March 31, 2015 was as follows (dollars in thousands):

	Unrecognized stock compensation expense		Weighted average remaining period (in years)
Employee stock options	$	13,821	2.79
Restricted stock	2,343		3.19
Total	$	16,164	2.85