Available-for-Sale Marketable Securities - Summary of Available-for-Sale Marketable Securities by Major Type of Security (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 219,734	$ 199,690
Gross Unrealized Gains	123	197
Gross Unrealized Losses	(50)	(27)
Estimated Fair Value	219,807	199,860
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,710	16,052
Gross Unrealized Gains	41	31
Gross Unrealized Losses	(1)	(2)
Estimated Fair Value	20,750	16,081
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,125	25,803
Gross Unrealized Gains	4	14
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	22,128	25,816
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	49,080	115,788
Gross Unrealized Gains	61	125
Gross Unrealized Losses	(23)	(23)
Estimated Fair Value	49,118	115,890
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	116,139	38,547
Gross Unrealized Gains	5	27
Gross Unrealized Losses	(17)	(1)
Estimated Fair Value	116,127	38,573
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,680	3,500
Gross Unrealized Gains	12
Gross Unrealized Losses	(8)
Estimated Fair Value	$ 11,684	$ 3,500