Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2016

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions

The fair market value of these stock options at the date of grant was estimated using the Black-Scholes option-pricing model with the following weighted average assumptions for the six months ended:

	June 30, 2016		June 30, 2015
Expected term	6 years, 1 month		6 years, 1 month
Interest rate	1.40	%	1.56	%
Dividend yield	—		—
Volatility (1)	92.4	%	103.3	%

(1) For the six months ended June 30, 2016, the Company estimated expected volatility based on the historical volatility of its own common stock on a stand-alone basis. Prior to January 1, 2016, including the six months ended June 30, 2015, the Company estimated expected volatility based on the historical volatility of a peer group.

Summary of Stock Option Activity

The following table summarizes stock option activity for the six months ended June 30, 2016:

($ in thousands except share and per share data)	Number of shares		Weighted- average exercise price		Weighted- average remaining contractual term	Aggregate intrinsic value
Outstanding at December 31, 2015	3,134,094		$	6.23	8 years	$	1,630
Granted	1,091,000		2.01
Exercised	—		—
Forfeited	(29,256	)	4.61
Expired	(188	)	4.24
Outstanding at June 30, 2016 (1)	4,195,650		$	5.15	8 years	$	43
Exercisable at June 30, 2016	1,954,190		$	7.50	6 years, 11 months	$	—

(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.