Stock-based Compensation (Employee and non-employee stock options outstanding) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014
Based Arrangements With Employees And Non employees [Line Items]
Options outstanding, Number	8,052,345
Options Exercisable, Number	6,172,691
Range One [Member]
Based Arrangements With Employees And Non employees [Line Items]
Exercise price, Lower Limit	$ 0.01
Exercise price, Upper Limit	$ 1.00
Options outstanding, Number	61,178
Options Exercisable, Number	61,178
Options Outstanding, Weighted Average Remaining Contractual Term	6 years 11 months 8 days
Range Two [Member]
Based Arrangements With Employees And Non employees [Line Items]
Exercise price, Lower Limit	$ 1.01
Exercise price, Upper Limit	$ 2.00
Options outstanding, Number	845,667
Options Exercisable, Number	754,001
Options Outstanding, Weighted Average Remaining Contractual Term	8 years 2 months 19 days
Range Three [Member]
Based Arrangements With Employees And Non employees [Line Items]
Exercise price, Lower Limit	$ 2.01
Exercise price, Upper Limit	$ 3.00
Options outstanding, Number	585,000
Options Exercisable, Number	337,082
Options Outstanding, Weighted Average Remaining Contractual Term	8 years 6 months 11 days
Range Four [Member]
Based Arrangements With Employees And Non employees [Line Items]
Exercise price, Lower Limit	$ 3.01
Exercise price, Upper Limit	$ 4.00
Options outstanding, Number	5,323,000
Options Exercisable, Number	4,066,263
Options Outstanding, Weighted Average Remaining Contractual Term	8 years 3 months 18 days
Range Five [Member]
Based Arrangements With Employees And Non employees [Line Items]
Exercise price, Lower Limit	$ 4.01
Exercise price, Upper Limit	$ 5.00
Options outstanding, Number	1,025,000
Options Exercisable, Number	741,667
Options Outstanding, Weighted Average Remaining Contractual Term	9 years 1 month 24 days
Range Six [Member]
Based Arrangements With Employees And Non employees [Line Items]
Exercise price, Lower Limit	$ 5.01
Exercise price, Upper Limit	$ 6.00
Options outstanding, Number	212,500
Options Exercisable, Number	212,500
Options Outstanding, Weighted Average Remaining Contractual Term	5 years 5 months 23 days