Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

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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)	2018		2017
Research and development	$	603	$	560
General and administrative		3,056		1,464
Stock-based compensation expense	$	3,659	$	2,024

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

For the three months ended March 31, 2018 and 2017, 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,
	2018	2017
Risk-free interest rate	2.56 - 2.74%	2.04 - 2.23%
Expected life in years	6	6
Expected volatility	80.75 - 81.10%	80.31 - 80.90%
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, 2018 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, 2017		3,852,135		$	5.12
Granted		7,500			4.27
Exercised		—			—
Cancelled		(36,667	)		5.93
Outstanding, March 31, 2018		3,822,968		$	5.08		6.20	$	1,020
Options exercisable, March 31, 2018		2,951,502		$	4.83		5.36	$	1,019
Options exercisable, December 31, 2017		2,925,502		$	5.12		5.58	$	1,152
Options available for future grant		403,962

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the three months ended March 31, 2018 is as follows:

	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2017		1,808,559		$	5.74
Granted		—			—
Vested		(205,491	)		5.38
Cancelled		(70,867	)		5.07
Non-vested, March 31, 2018		1,532,201		$	5.82