Summary of Significant Accounting Policies - Schedule of Estimated Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 488	$ 941	$ 1,205	$ 1,989
Research and development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	135	112	256	198
General and administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 353	$ 829	$ 949	$ 1,791