Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)		12 Months Ended
	Jan. 27, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 31, 2018
Fair Value of Assets and Liabilities Measured on Non Recurring Basis [Line Items]
Fair value input transfer between levels		$ 0	$ 0
Increase in fair value of derivative		(1,629,000)	$ (283,000)	$ (39,000)
IPO [Member]
Fair Value of Assets and Liabilities Measured on Non Recurring Basis [Line Items]
Dilution payment					$ 2,000,000
License Agreement [Member]
Fair Value of Assets and Liabilities Measured on Non Recurring Basis [Line Items]
Provision for maximum cash payment	$ 2,000,000	$ 2,000,000
License Agreement [Member] | Research and Development Expense [Member]
Fair Value of Assets and Liabilities Measured on Non Recurring Basis [Line Items]
Initial fair value of the derivative	$ 49,000
License Agreement [Member] | Stock Purchase Agreement [Member]
Fair Value of Assets and Liabilities Measured on Non Recurring Basis [Line Items]
Common stock issued for initial consideration for license	1,161,665