Warrants - Summary of Warrants Outstanding (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Warrant or Right [Line Items]
Warrants Outstanding	26,538,593	7,371,925	2,177,425
Class One [Member]
Class of Warrant or Right [Line Items]
Exercise Price	$ 3.10
Warrants Outstanding	48,387
Expiration Date	Sep. 19, 2022
Class Two [Member]
Class of Warrant or Right [Line Items]
Exercise Price	$ 2.00
Warrants Outstanding	900,000
Expiration Date	Apr. 10, 2023
Class Three [Member]
Class of Warrant or Right [Line Items]
Exercise Price	$ 3.10
Warrants Outstanding	462,106
Expiration Date	May 10, 2024
Class Four [Member]
Class of Warrant or Right [Line Items]
Exercise Price	$ 3.10
Warrants Outstanding	602,414
Expiration Date	Jul. 25, 2024
Class Five [Member]
Class of Warrant or Right [Line Items]
Exercise Price	$ 3.10
Warrants Outstanding	1,064,518
Expiration Date	Nov. 08, 2024
Class Six [Member]
Class of Warrant or Right [Line Items]
Exercise Price	$ 1.00
Warrants Outstanding	4,294,500
Expiration Date	Jul. 17, 2025
Class Seven [Member]
Class of Warrant or Right [Line Items]
Exercise Price	$ 0.75
Warrants Outstanding	9,583,334
Class Eight [Member]
Class of Warrant or Right [Line Items]
Exercise Price	$ 0.90
Warrants Outstanding	9,583,334
Expiration Date	Mar. 25, 2024