Net Loss per Share of Common Stock - Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Shares Outstanding (Parenthetical) (Detail) (USD $)	Mar. 31, 2014	Sep. 30, 2014 Warrants to purchase convertible preferred stock [Member]	Sep. 30, 2013 Warrants to purchase convertible preferred stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Warrants to purchase convertible preferred stock, exercise price	$ 5.17	$ 5.17	$ 5.17