Warrants - Summary of Change in Warrant (Detail) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Class of Warrant or Right [Line Items]
Weighted Average Remaining Contractual Life, Exercised	8 years 2 months 12 days
Warrants Not Settleable in Cash
Class of Warrant or Right [Line Items]
Number of Warrants, Outstanding, Beginning balance	4,329,437
Number of Warrants, Exercised	(200,000)
Number of Warrants, Outstanding, Ending balance	4,129,437	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, Outstanding (in dollars per share), Ending balance	$ 1.03	$ 1.03
Weighted Average Remaining Contractual Life, Outstanding	3 years	3 years 8 months 12 days
Weighted Average Fair Value, Outstanding, Beginning balance (in dollars per share)	$ 0.26
Weighted Average Fair Value, Outstanding, Ending balance (in dollars per share)	$ 0.22	$ 0.26