Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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 June 30,				For the six months ended June 30,
(in thousands)	2018		2017		2018		2017
Research and development	$	609	$	596	$	1,212	$	1,156
General and administrative		1,102		1,462		4,158		2,926

Stock-based compensation expense	$	1,711	$	2,058	$	5,370	$	4,082

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

For the three months ended June 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 June 30,
	2018	2017
Risk-free interest rate	2.66 - 2.91%	1.85 - 2.05%
Expected life in years	6	6
Expected volatility	81.48 - 81.66%	80.93 - 81.03%
Expected dividend yield	0	0

Stock Option Activity under Stock Option Plan

Stock option activity under the Company’s stock option plan for the six months ended June 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		205,500			4.32
Exercised		(104,167	)		2.30
Cancelled		(149,666	)		5.50

Outstanding, June 30, 2018		3,803,802		$	5.08		6.14	$	415

Options exercisable, June 30, 2018		2,840,835		$	4.97		5.16	$	415

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

Options available for future grant		318,961

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the six months ended June 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		(538,824	)		7.84
Cancelled		(70,867	)		5.07

Non-vested, June 30, 2018		1,198,868		$	4.83