Accumulated Other Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax, from Unrealized Gains (Losses) on Available-for-Sale Marketable Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	$ 186,713	$ 133,630	$ 86,780
Amount reclassified from accumulated other comprehensive income	(272)		5
Net current period other comprehensive income (loss)	(97)	284	(44)
Balance, Value	249,001	186,713	133,630
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	170	(114)	(70)
Other comprehensive income (loss) before reclassifications	175	284	(49)
Amount reclassified from accumulated other comprehensive income	(272)		5
Net current period other comprehensive income (loss)	(97)	284	(44)
Balance, Value	$ 73	$ 170	$ (114)