Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Cash and Cash Equivalents | Money Market Securities
Asset included in:
Financial Assets	$ 2,573,882	$ 3,608,890
Investments at Fair Value | US Government Obligations
Asset included in:
Financial Assets	3,308,573
Investments at Fair Value | US Government Agency Obligations
Asset included in:
Financial Assets	14,715,616
Investments at Fair Value | Corporate Debt Securities
Asset included in:
Financial Assets	18,454,522
Convertible Preferred Stock Warrants
Liabilities included in:
Financial Liabilities		429,035
Warrant
Liabilities included in:
Financial Liabilities		301,508
Level 1 | Cash and Cash Equivalents | Money Market Securities
Asset included in:
Financial Assets	2,573,882	3,608,890
Level 1 | Investments at Fair Value | US Government Obligations
Asset included in:
Financial Assets	3,308,573
Level 2 | Investments at Fair Value | US Government Agency Obligations
Asset included in:
Financial Assets	14,715,616
Level 2 | Investments at Fair Value | Corporate Debt Securities
Asset included in:
Financial Assets	$ 18,454,522
Level 3 | Convertible Preferred Stock Warrants
Liabilities included in:
Financial Liabilities		429,035
Level 3 | Warrant
Liabilities included in:
Financial Liabilities		$ 301,508