Stockholders' Equity - Summary of Warrants Issued and Outstanding (Detail)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Class Of Warrant Or Right [Line Items]
Shares of Common Stock	1,733,565
Exercisable Warrants [Member]
Class Of Warrant Or Right [Line Items]
Shares of Common Stock	1,733,565
Exercisable Warrants [Member] | Warrants One [Member]
Class Of Warrant Or Right [Line Items]
Date of Issuance	Sep. 24, 2014
Date of Expiration	Sep. 24, 2019
Exercise Price | $ / shares	$ 20.00
Shares of Common Stock	1,125,005
Exercisable Warrants [Member] | Warrants Two [Member]
Class Of Warrant Or Right [Line Items]
Date of Issuance	Oct. 20, 2014
Date of Expiration	Oct. 20, 2019
Exercise Price | $ / shares	$ 20.00
Shares of Common Stock	87,500
Exercisable Warrants [Member] | Warrants Three [Member]
Class Of Warrant Or Right [Line Items]
Date of Issuance	Mar. 30, 2016
Date of Expiration	Mar. 30, 2021
Exercise Price | $ / shares	$ 3.88
Shares of Common Stock	521,060