Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2012

Share-Based Payments

Schedule of stock-based compensation recognized related to the grant of employee and non-employee stock options, and non-vested stock

	Year Ended December 31,
	2010		2011			2012
	(in thousands)
Research and development	$	53	$	63		$	208
Selling, general and administrative		244		(145	)		131
Total	$	297	$	(82	)	$	339

Schedule of assumptions used in estimation of fair value of each award option on the date of grant using Black-Scholes option-pricing model

	Year Ended December 31,
	2010	2011	2012
Fair value of common stock	$1.60 - $7.04	$2.56 - $3.36	$5.07 - $12.92
Expected volatility	60.3% - 61.5%	59.1% - 74.7%	68.3% - 71.6%
Dividend Yield	0%	0%	0%
Expected term	6.25 years	0.41 - 6.25 years	6.25 years
Risk-free rate	1.65% - 2.72%	0.15% - 2.93%	0.89% - 1.14%
Expected forfeiture rate	5%	0% - 5%	0% - 5%

Summary of stock option activity under the 2005 Plan and the 2012 Plan

	Number of Options			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term
Outstanding, December 31, 2010		664,479		$	1.72		7.83
Granted		144,750		$	5.80
Exercised		(69,559	)	$	0.40
Forfeited or expired		(141,561	)	$	2.17
Outstanding, December 31, 2011		598,109		$	2.75		7.71
Granted		188,136		$	10.73
Exercised		(159,264	)	$	1.67
Forfeited or expired		(57,070	)	$	2.45
Outstanding, December 31, 2012		569,911		$	5.72		7.88
As of December 31, 2012:
Vested and expected to vest		564,083		$	5.72		7.87
Exercisable		200,312		$	2.11		5.73