Commitments and Contingencies - Consulting Agreement - Additional Information (Detail) - Consulting Agreement [Member] - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense		$ 0	$ 0	$ 0
Milestone payments		0	$ 0	$ 0
Clinical Development and Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Shares of common stock for attaining milestones	126,984
Research and development expense related to milestone expense		1,800,000
Milestone payments		500,000
Payments for stock issued upon reaching a milestone		$ 1,300,000
Milestone based share compensation, shares issued		39,681
Clinical Development and Regulatory Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 2,000,000