Warrants - Summary of Change in Warrant (Detail) - Warrants Not Settleable in Cash - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Class of Warrant or Right [Line Items]
Number of Warrants, Outstanding, Beginning balance (in shares)	4,329,437
Number of Warrants, Exercised (in shares)	(200,000)
Number of Warrants, Reserved for future issuance (in shares)	1,336,326
Number of Warrants, Outstanding, Ending balance (in shares)	5,465,763	4,329,437
Weighted Average Exercise Price, Outstanding (in dollars per share), Beginning balance	$ 1.03
Weighted Average Exercise Price, Exercised (in dollars per share)	1.00
Weighted Average Exercise Price, Reserved for future issuance (in dollars per share)	0.67
Weighted Average Exercise Price, Outstanding (in dollars per share), Ending balance	$ 0.78	$ 1.03
Weighted Average Remaining Contractual Life, Outstanding	2 years 8 months 12 days	3 years 8 months 12 days
Weighted Average Remaining Contractual Life, Exercised	8 years 2 months 12 days
Weighted Average Remaining Contractual Life, Reserved for future issuance	2 years 7 months 6 days
Weighted Average Fair Value, Outstanding, Beginning balance (in dollars per share)	$ 0.26
Weighted Average Fair Value, Reserved for future issuance (in dollars per share)	0.20
Weighted Average Fair Value, Outstanding, Ending balance (in dollars per share)	$ 0.22	$ 0.26