Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

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)	2018		2017		2018		2017
Research and development	$	552	$	615	$	1,765	$	1,772
General and administrative		928		1,467		5,085		4,393

Stock-based compensation expense	$	1,480	$	2,082	$	6,850	$	6,165

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

For the three months ended September 30, 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 September 30,
	2018	2017
Risk-free interest rate	2.82 - 2.98%	1.88 - 2.01%
Expected life in years	6	6
Expected volatility	82.27 - 83.08%	80.82 - 80.95%
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, 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		506,000			3.50
Exercised		(104,167	)		2.30
Cancelled		(184,500	)		5.77

Outstanding, September 30, 2018		4,069,468		$	5.24		6.17	$	576

Options exercisable, September 30, 2018		2,924,501		$	5.13		4.98	$	498

Options exercisable, December 31, 2017		2,925,502		$	5.12		5.58	$	1,152

Options available for future grant		5,053,295

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the nine months ended September 30, 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		(573,340	)		7.61
Cancelled		(70,867	)		5.07

Non-vested, September 30, 2018		1,164,352		$	4.85