Common Stock Equity Incentive Plan (Tables)

12 Months Ended

Dec. 31, 2012

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

The following table summarizes the stock option activity for the year ended December 31, 2012:



	Number of options		Weighted average exercise price		Weighted average remaining contractual term (years)
Outstanding at beginning of period	3,515,051		$	3.51
Options granted	672,079		8.10
Options exercised	(341,429	)	2.60
Options forfeited	(86,296	)	6.88
Options expired	(6,992	)	2.94
Outstanding at end of period	3,752,413		$	4.34	7.2
Options exercisable at end of period	2,571,041		$	3.34	6.7

Assumptions Used in Black-Scholes Pricing Model for New Grants

The following table summarizes options that were granted during the years ended December 31, 2012, 2011 and 2010, and the range of assumptions used to estimate the fair value of those stock options using a Black-Scholes valuation model:



	Years Ended December 31,
	2012	2011	2010
Number of options granted	672,079	664,323	1,297,738
Risk-free interest rate	0.98%-2.05%	0.1%-3.1%	2.3%-3.5%
Expected dividend yield	—	—	—
Expected volatility	63.0%-73.6%	62.6%-67.9%	59.8%-68.1%
Expected term (in years)	5.8-7.0	5.0-7.5	5.0-7.5
Weighted average grant-date fair value per share	$5.02	$7.12	$2.90