Formation and Business of the Company - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 01, 2016	Jul. 31, 2016	Jun. 30, 2019	Jun. 30, 2019
Grant [Line Items]
Revenue from product development award			$ 3,054,000	$ 4,753,000
Cancer Prevention & Research Institute of Texas [Member]
Grant [Line Items]
Revenue from product development award		$ 20,000,000
Grant termination date	Nov. 30, 2019
Percentage of cash required to raise in matching funds	50.00%
Cash required to raise in matching funds	$ 10,000,000
Term of project during which cash required to raise in matching funds	3 years
Cash required in matching funds raised	$ 10,000,000
Percentage of grant award proceeds required to pay	400.00%
Cancer Prevention & Research Institute of Texas [Member] | Maximum [Member]
Grant [Line Items]
Percentage of grant award proceeds required to pay thereafter until government exclusivity maintained	1.00%
Stanford University [Member] | Maximum [Member]
Grant [Line Items]
Milestone payments upon achievement of clinical and regulatory milestones			$ 1,000,000	$ 1,000,000