Stock-Based Compensation (Details) (Employee Consultant and Non Employee Director Stock Option [Member], USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Employee Consultant and Non Employee Director Stock Option [Member]
Shares
Options Outstanding at beginning of the period (in shares)	5,770,544
Granted (in shares)	1,333,850
Exercised (in shares)	(134,131)
Canceled (in shares)	(8,497)
Options Outstanding at the end of the period (in shares)	6,961,766	5,770,544
Options Vested and Expected to Vest at the end of the period (in shares)	6,886,817
Options Exercisable at the end of the period (in shares)	3,480,200
Shares Available for Grant under the 2008 Plan (in shares)	765,589
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 8.17
Granted (in dollars per share)	$ 13.57
Exercised (in dollars per share)	$ 6.05
Canceled (in dollars per share)	$ 10.51
Options Outstanding at the end of the period (in dollars per share)	$ 9.24	$ 8.17
Options Vested and Expected to Vest at the end of the period (in dollars per share)	$ 9.19
Options Exercisable at the end of the period (in dollars per share)	$ 6.18
Weighted Average Remaining Contractual Term
Options Outstanding at beginning of the period	7 years 2 months 12 days	7 years
Options Outstanding at the end of the period	7 years 2 months 12 days	7 years
Options Vested and Expected to Vest at the end of the period	7 years 2 months 12 days
Options Exercisable at the end of the period	5 years 3 months 18 days
Additional information
Weighted average grant-date fair value (in dollars per share)	$ 8.76