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	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	$ 160,474	$ 186,713	$ 114,522	$ 133,630	$ 186,713	$ 133,630
Other comprehensive income before reclassifications					525	279
Amount reclassified from accumulated other comprehensive income	(60)				(60)
Net current period other comprehensive income	703	(238)	92	187	465	279
Balance, Value	140,928	160,474	99,545	114,522	140,928	99,545
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance, Value	(68)	170	73	(114)	170	(114)
Net current period other comprehensive income	703	(238)	92	187
Balance, Value	$ 635	$ (68)	$ 165	$ 73	$ 635	$ 165