Stock-Based Compensation (Details) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended	9 Months Ended		1 Months Ended		9 Months Ended
	Sep. 30, 2013 Stock option	Sep. 30, 2012 Stock option	Sep. 30, 2013 Stock option	Sep. 30, 2012 Stock option	Jan. 31, 2013 Stock option Director	Sep. 30, 2013 Restricted stock awards	Sep. 30, 2012 Restricted stock awards	Jan. 31, 2013 2006 Stock Plan	Sep. 30, 2013 2006 Stock Plan	Sep. 30, 2013 2006 Stock Plan Stock option Maximum
Stock-Based Compensation
Number of shares reserved for issuance before annual increase								7,700,000
Shares reserved for issuance								9,000,000
Increase in number of shares reserved for issuance								1,300,000
Percentage of outstanding shares of common stock used to compute annual increase in number of shares reserved for issuance								5.00%
Expiration period										10 years
Vesting period										4 years
Shares available for future issuance									1,628,225
Shares
Outstanding at the beginning of the period (in shares)			5,521,584
Options granted (in shares)			1,801,079
Options exercised (in shares)			(132,991)		(114,250)
Options cancelled (in shares)			(453,463)
Outstanding at the end of the period (in shares)	6,736,209		6,736,209
Exercisable at the end of the period (in shares)	3,662,767		3,662,767
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)			$ 6.40
Options granted (in dollars per share)			$ 9.53
Options exercised (in dollars per share)			$ 8.14
Options cancelled (in dollars per share)			$ 9.88
Outstanding at the end of the period (in dollars per share)	$ 6.97		$ 6.97
Exercisable at the end of the period (in dollars per share)	$ 6.61		$ 6.61
Additional disclosures
Total cash received from stock option exercises			$ 1,100,000	$ 900,000
Proceeds resulting from exercise of stock options					990,000
Weighted-average grant date fair value of options (in dollars per share)	$ 4.21	$ 6.00	$ 7.65	$ 4.04
Total fair value of restricted stock vested during the period						$ 200,000	$ 400,000
Shares
Outstanding at the beginning of the period (in shares)						35,122
Vested (in shares)						(32,622)
Granted (in shares)						115,000
Forfeited (in shares)						(75,000)
Outstanding at the end of the period (in shares)						42,500
Weighted average grant date fair value
Outstanding at the beginning of the period (in dollars per share)						$ 5.04
Vested (in dollars per share)						$ 5.33
Granted (in dollars per share)						$ 7.99
Forfeited (in dollars per share)						$ 9.59
Outstanding at the end of the period (in dollars per share)						$ 4.78
Weighted average assumptions used to estimate fair value of each employee stock option award
Risk-free interest rate (as a percent)	1.74%	0.92%	1.12%	1.11%
Expected life in years	6 years 3 months	6 years 2 months 23 days	6 years 3 months	6 years 2 months 26 days
Volatility (as a percent)	103.00%	102.00%	102.00%	101.00%