Income Taxes - Total Balance of Unrecognized Gross Tax Benefits Resulting from R&D Credits Claimed (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 4,212	$ 2,830	$ 2,168
Additions based on current year tax positions	4,959	1,382	662
Unrecognized tax benefits at end of year	$ 9,171	$ 4,212	$ 2,830