Commitments and Contingencies - University of California License Agreements - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2015	Jun. 30, 2015	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2015
Regulatory and Sales Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense					$ 300,000
Milestone payments					300,000
University of California License Agreements [Member]
Commitments And Contingencies [Line Items]
Upfront payment		$ 50,000
Annual license maintenance fee							$ 15,000
Research and development expense related to milestone expense			$ 0	$ 0	200,000	$ 0
Milestone payments			$ 0	$ 0	$ 200,000	$ 0
University of California License Agreements [Member] | After The Effective Date [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum	27 years
University of California License Agreements [Member] | After The First Sale [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum	15 years
University of California License Agreements [Member] | Clinical Development [Member]
Commitments And Contingencies [Line Items]
Milestone payments	$ 100,000
University of California License Agreements [Member] | Clinical Development [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Percentage of net sales paid as royalties	1.00%
University of California License Agreements [Member] | Regulatory Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments		700,000
University of California License Agreements [Member] | Sales Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments		$ 2,000,000