Commitments and Contingencies - University of California License Agreements - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended	31 Months Ended
	Dec. 31, 2015	Jun. 30, 2015	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2015	Dec. 31, 2017
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			$ 200,000	$ 0	200,000	$ 0
Milestone payments			$ 200,000	$ 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
Additional milestone payments								$ 0
University of California License Agreements [Member] | Sales Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments		$ 2,000,000
Additional milestone payments								$ 0