Balance Sheet Components - Schedule of Accrued Expenses And Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Balance Sheet Components [Abstract]
Accrued pre-clinical expenses	$ 675	$ 537
Accrued professional fees	159	41
Accrued payroll and benefits	256	348
Accrued taxes	50	154
Accrued construction in progress	330	589
Other current liabilities	646	39
Total	$ 2,116	$ 1,708