Preferred Stock, Common Stock and Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail)	Dec. 31, 2014	Dec. 31, 2013
Common Stock Reserved for Future Issuance [Line Items]
Total common stock reserved for future issuance	1,043,457	769,250
Stock Options [Member]
Common Stock Reserved for Future Issuance [Line Items]
Total common stock reserved for future issuance	683,500	624,750
Authorized for future option grants [Member]
Common Stock Reserved for Future Issuance [Line Items]
Total common stock reserved for future issuance	188,370	8,500
Warrants to purchase common stock [Member]
Common Stock Reserved for Future Issuance [Line Items]
Total common stock reserved for future issuance	118,881	106,000
Authorized for Employee Stock Purchase Plan [Member]
Common Stock Reserved for Future Issuance [Line Items]
Total common stock reserved for future issuance	52,706	30,000