Accounting for Shared-Based Payments (Tables)

3 Months Ended

Mar. 31, 2015

Accounting for Shared-Based Payments

Schedule of stock-based compensation expense

	Three Months Ended March 31,
($ in thousands)	2015		2014
Research and development	$	530	$	432
General and administrative	1,875		832
Total stock-based compensation expense	$	2,405	$	1,264

Schedule of weighted-average assumptions used to estimate fair value of stock option awards using the Black-Scholes option valuation model

	Three Months Ended March 31, 2015	Three Months Ended March 31, 2014
Risk-free interest rate	1.46%-2.02%	1.94%-2.52%
Dividend yield	—	—
Expected volatility	57%	60%
Expected term (in years)	6 years	6-9.3 years

Summary of stock option activity and of changes in stock options outstanding under the Plan

	Number of Options		Exercise Price Per Share		Weighted Average Exercise Price Per Share		Intrinsic Value (in thousands)		Weighted Average Remaining Contractual Term
Balance outstanding, December 31, 2014(1)	16,567,020		$	0.44-17.79	$	3.20	$	8,949	7.29 years
Granted	135,000		$	2.94-3.33	$	3.04
Exercised	—		$	—	$	—
Forfeited	(80,955	)	$	8.34 – 9.45	$	9.26
Balance outstanding, March 31, 2015(1)	16,621,065		$	0.44 - 17.79	$	3.16	$	26,233	7.09 years
Exercisable, at March 31, 2015	7,232,742		$	0.44 - 17.79	$	3.12	$	11,808	5.81 years

(1)          Number of options represented above includes 4,364,000 options vesting upon a change of control, granted during the years ended December 31, 2009 and 2010, at an exercise price of $0.70 per share. Because the probability of a change of control transaction is not predictable no stock based compensation expense associated with these options has been recognized since the grant date.