Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

Text Block [Abstract]

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 March 31,
(in thousands)	2019		2018
Research and development	$	433	$	603
General and administrative		1,023		3,056
Stock-based compensation expense	$	1,456	$	3,659

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

For the three months ended March 31, 2019 and 2018, 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 March 31,
	2019	2018
Risk-free interest rate	2.28 - 2.53%	2.56 - 2.74%
Expected life in years	6 - 6.25	6
Expected volatility	78.87 - 85.00%	80.75 - 81.10%
Expected dividend yield	0	0

Stock Option Activity under Stock Option Plan

Stock option activity under the Company’s stock option plan for the three months ended March 31, 2019 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, 2018		5,277,085		$	4.24
Granted		1,496,333			2.24
Exercised		—			—
Cancelled		(1,357,333	)		4.33
Outstanding, March 31, 2019		5,416,085		$	3.66		7.82	$	5,494
Options exercisable, March 31, 2019		2,213,008		$	5.14		5.33	$	1,025
Options exercisable, December 31, 2018		3,099,935		$	5.15		4.93	$	88
Options available for future grant		3,996,638

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the three months ended March 31, 2019 is as follows:

	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2018		682,070		$	3.47
Granted		1,393,536			2.24
Vested		(446,428	)		2.24
Cancelled		(7,333	)		4.14
Non-vested, March 31, 2019		1,621,845		$	2.92