Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Stock-Based Compensation

Schedule of stock-based compensation expense attributable to share-based payments made to employees and directors and included in operating expenses

	Three Months Ended
	March 31,
(in thousands)	2018		2017
Stock-based compensation:
Research and development
Employee Stock Purchase Plans	$	22	$	22
Equity Incentive Plans		556		714
	$	578	$	736
General and administrative
Employee Stock Purchase Plans	$	14	$	19
Equity Incentive Plans		997		1,029
	$	1,011	$	1,048
Total stock-based compensation expense	$	1,589	$	1,784

Schedule of weighted average assumptions applied to options

	Three Months Ended
	March 31,
	2018		2017
Average risk free interest rate		2.1%		1.7%
Expected dividend yield		—		—
Expected lives (years)		3.8		3.9
Expected volatility		74.9%		86.9%
Weighted average exercise price (per share)	$	2.24	$	1.59

Schedule of information related to outstanding and exercisable options

($ in thousands, except per share data)	Stock Options	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value
Outstanding at December 31, 2017	21,402,200	$	2.94	6.5	$	5,805
Granted	4,116,800		2.24
Exercised	—		—
Forfeited	(894,377)		2.46
Expired	(407,075)		11.09
Outstanding at March 31, 2018 (1)	24,217,548	$	2.70	6.7	$	3,716
Exercisable at March 31, 2018	14,734,826	$	2.95	5.4	$	2,998

(1) Includes both vested stock options as well as unvested stock options for which the requisite service period has not been rendered but that are expected to vest based on achievement of a service condition.