Commitments and Contingencies - Consulting Agreement - Additional Information (Detail) - Consulting Agreement [Member]	1 Months Ended	12 Months Ended
	Jan. 31, 2014 USD ($) shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) Milestone shares	Dec. 31, 2014 USD ($) Milestone shares
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense		$ 0	$ 0
Milestone payments		$ 0	$ 0
Clinical Development and Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Shares of common stock for attaining milestones | shares	126,984
Clinical Development and Regulatory Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 2,000,000
First Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Milestones achieved | Milestone					2
Research and development expense related to milestone expense					$ 200,000
Milestone payments					50,000
Payments for stock issued upon reaching a milestone					$ 100,000
Milestone based share compensation, shares issued | shares					15,872
Second Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Milestones achieved | Milestone				1
Research and development expense related to milestone expense				$ 1,700,000
Milestone payments				500,000
Payments for stock issued upon reaching a milestone				$ 1,200,000
Milestone based share compensation, shares issued | shares				23,809
Third Clinical Development Milestones [Member]
Commitments And Contingencies [Line Items]
Milestones achieved | Milestone				1
Research and development expense related to milestone expense				$ 1,700,000
Milestone payments				500,000
Payments for stock issued upon reaching a milestone				$ 1,200,000
Milestone based share compensation, shares issued | shares				23,809