Warrants - Summary of the Warrants Outstanding (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Warrants Issued [Member]
Class of Warrant or Right [Line Items]
Warrants, Issue Date	Dec. 03, 2018
Warrants, Classification	Equity
Warrants, Exercise Price	$ 3.90
Warrants, Expiration Date	Jun. 03, 2024
Warrants Outstanding	937,500
Prefunded Warrants Issued [Member]
Class of Warrant or Right [Line Items]
Warrants, Issue Date	Dec. 03, 2018
Warrants, Classification	Equity
Warrants, Exercise Price	$ 3.20
Warrants Outstanding	697,500
Public Offering One [Member]
Class of Warrant or Right [Line Items]
Warrants, Issue Date	Apr. 03, 2018
Warrants, Classification	Equity
Warrants, Exercise Price	$ 7.50
Warrants, Expiration Date	Apr. 03, 2023
Warrants Outstanding	2,407,500
Public Offering Two [Member]
Class of Warrant or Right [Line Items]
Warrants, Issue Date	Apr. 04, 2018
Warrants, Classification	Equity
Warrants, Exercise Price	$ 7.50
Warrants, Expiration Date	Apr. 04, 2023
Warrants Outstanding	57,500
Private Placement Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants, Issue Date	Jun. 15, 2015
Warrants, Classification	Equity
Warrants, Exercise Price	$ 75.50
Warrants, Expiration Date	Jun. 15, 2020
Warrants Outstanding	319,003	319,003
Hercules Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants, Issue Date	Jun. 15, 2015
Warrants, Classification	Equity
Warrants, Exercise Price	$ 83.50
Warrants, Expiration Date	Jun. 16, 2020
Warrants Outstanding	2,515	2,515
MTS Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants, Issue Date	Aug. 31, 2015
Warrants, Classification	Equity
Warrants, Exercise Price	$ 118.00
Warrants, Expiration Date	Aug. 31, 2020
Warrants Outstanding	3,000	3,000
Representative's Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants, Issue Date	Mar. 21, 2014
Warrants, Classification	Equity
Warrants, Exercise Price	$ 226.60
Warrants, Expiration Date	Mar. 21, 2019
Warrants Outstanding	3,710	3,710
Underwriter's Warrants [Member]
Class of Warrant or Right [Line Items]
Warrants, Issue Date	Mar. 21, 2014
Warrants, Classification	Equity
Warrants, Exercise Price	$ 226.60
Warrants, Expiration Date	Mar. 21, 2019
Warrants Outstanding	216	216