Formation and Business of the Company - Additional Information (Detail) - USD ($)			1 Months Ended	3 Months Ended
	May 07, 2019	Jun. 01, 2016	Jul. 31, 2016	Mar. 31, 2019
Grant [Line Items]
Revenue from product development award				$ 1,699,000
Cancer Prevention & Research Institute of Texas [Member]
Grant [Line Items]
Revenue from product development award			$ 20,000,000
Initial grant termination date		May 31, 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%
Cancer Prevention & Research Institute of Texas [Member] | Subsequent Event [Member]
Grant [Line Items]
Extension of grant termination date	Nov. 30, 2019
Stanford University [Member] | Maximum [Member]
Grant [Line Items]
Milestone payments upon achievement of clinical and regulatory milestones				$ 1,000,000