Stock-Based Compensation (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014
Stock Options Outstanding
Number of shares	6,664,359
Weighted average remaining contractual life	5 years 9 months
Weighted average exercise price per share (in dollars per share)	$ 4.70
Stock Options Exercisable
Number of shares	4,416,231
Weighted average exercise price per share (in dollars per share)	$ 6.30
$0.55 - 1.29
Stock-based compensation
Exercise price, minimum (in dollars per share)	$ 0.55
Exercise price, maximum (in dollars per share)	$ 1.29
Stock Options Outstanding
Number of shares	627,796
Weighted average remaining contractual life	8 years 10 months 6 days
Weighted average exercise price per share (in dollars per share)	$ 1.19
Stock Options Exercisable
Number of shares	197,338
Weighted average exercise price per share (in dollars per share)	$ 1.24
1.33 - 1.33
Stock-based compensation
Exercise price, minimum (in dollars per share)	$ 1.33
Exercise price, maximum (in dollars per share)	$ 1.33
Stock Options Outstanding
Number of shares	1,150,000
Weighted average remaining contractual life	8 years 11 months 19 days
Weighted average exercise price per share (in dollars per share)	$ 1.33
Stock Options Exercisable
Number of shares	0
Weighted average exercise price per share (in dollars per share)	$ 0.00
1.34 - 1.64
Stock-based compensation
Exercise price, minimum (in dollars per share)	$ 1.34
Exercise price, maximum (in dollars per share)	$ 1.64
Stock Options Outstanding
Number of shares	1,108,193
Weighted average remaining contractual life	5 years 6 months 29 days
Weighted average exercise price per share (in dollars per share)	$ 1.54
Stock Options Exercisable
Number of shares	983,855
Weighted average exercise price per share (in dollars per share)	$ 1.55
1.65 - 2.66
Stock-based compensation
Exercise price, minimum (in dollars per share)	$ 1.65
Exercise price, maximum (in dollars per share)	$ 2.66
Stock Options Outstanding
Number of shares	1,622,301
Weighted average remaining contractual life	5 years 8 months 5 days
Weighted average exercise price per share (in dollars per share)	$ 2.15
Stock Options Exercisable
Number of shares	1,124,512
Weighted average exercise price per share (in dollars per share)	$ 2.19
2.72 - 9.77
Stock-based compensation
Exercise price, minimum (in dollars per share)	$ 2.72
Exercise price, maximum (in dollars per share)	$ 9.77
Stock Options Outstanding
Number of shares	1,115,402
Weighted average remaining contractual life	3 years 8 months 23 days
Weighted average exercise price per share (in dollars per share)	$ 7.54
Stock Options Exercisable
Number of shares	1,069,859
Weighted average exercise price per share (in dollars per share)	$ 7.60
10.08 - 24.97
Stock-based compensation
Exercise price, minimum (in dollars per share)	$ 10.08
Exercise price, maximum (in dollars per share)	$ 24.97
Stock Options Outstanding
Number of shares	1,040,667
Weighted average remaining contractual life	2 years 9 months 22 days
Weighted average exercise price per share (in dollars per share)	$ 14.85
Stock Options Exercisable
Number of shares	1,040,667
Weighted average exercise price per share (in dollars per share)	$ 14.85