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, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	$ 133,630	$ 86,780	$ 50,725
Other comprehensive income before reclassifications	284	(49)	(68)
Amount reclassified from accumulated other comprehensive loss (income)		5	(5)
Net current period other comprehensive income	284	(44)	(73)
Balance, Value	186,713	133,630	86,780
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	(114)	(70)	3
Net current period other comprehensive income	284	(44)	(73)
Balance, Value	$ 170	$ (114)	$ (70)