Accounting for Shared-Based Payments (Tables)

12 Months Ended

Dec. 31, 2012

Accounting for Shared-Based Payments

Schedule of stock-based compensation expense

	Years Ended December 31,						November 15, 2005 (inception) to
	2012		2011		2010		December 31, 2012
	(dollars in thousands)
Employees—included in research and development	$	975	$	107	$	188	$	1,602
Employees—included in general and administrative	635		93		210		1,409
Subtotal employee stock based compensation	1,610		200		398		3,011
Non-employees—included in research and development	128		73		52		296
Non-employees—included in general and administrative	777		549		262		2,177
Subtotal non-employee stock based compensation	905		622		314		2,473
Total stock-based compensation expense	$	2,515	$	822	$	712	$	5,484

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

	Years Ended December 31,
	2012	2011	2010
Risk-free interest rate	0.85%-1.5%	0.88%-1.25%	2.31%-2.71%
Dividend yield	—	—	—
Expected volatility	60%	70%	90%
Expected term (in years)	6.0 yrs.	6.0 yrs.	6.0 yrs.

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

	Number of Options(1)		Exercise Price Per Share		Weighted Average Exercise Price Per Share		Intrinsic Value(in thousands)
Balance outstanding, January 1, 2010	2,107,008		$	0.50-1.90	$	0.61	$	22,320
Granted (2)	2,232,500		$	1.40	$	1.40
Exercised	—		—		—
Forfeited	(37,500	)	$	1.40	$	1.40
Balance outstanding, January 1, 2011	4,302,008		$	0.50-1.90	$	1.04	$	25,763
Granted	1,807,000		$	3.35-4.30	$	3.50
Exercised	—		—		—
Forfeited	(144,969	)	$	0.50-1.40	$	1.04
Balance outstanding, December 31, 2011	5,964,039		$	0.50-4.30	$	1.77	$	6,027
Granted	3,875,229		$	3.40-5.20	$	4.29
Exercised	—		—		—
Forfeited	(105,000	)	$	3.40-4.38	$	4.10
Balance outstanding, December 31, 2012	9,734,268		$	0.50-5.20	$	2.75	$	24,482
Exercisable at December 31, 2012	2,726,302		$	0.50-5.20	$	1.42	$	10,464

(1) Number of shares outstanding represented above reflect a retroactive change of a one for two (1:2) reverse stock split effective on November 30, 2011.

(2) Contingent vesting upon change of control. The Fair Value at the date of grant was approximately $30,244,000 determined using the Black-Scholes option valuation model assumptions discussed above. No stock based compensation expense associated with these options was recognized since the grant date.