Available-for-Sale Marketable Securities - Summary of Available-for-Sale Marketable Securities by Major Type of Security (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 199,690	$ 167,812
Gross Unrealized Gains	197	5
Gross Unrealized Losses	(27)	(119)
Estimated Fair Value	199,860	167,698
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,052	19,540
Gross Unrealized Gains	31
Gross Unrealized Losses	(2)	(1)
Estimated Fair Value	16,081	19,539
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	25,803	17,860
Gross Unrealized Gains	14
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	25,816	17,859
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	115,788	75,999
Gross Unrealized Gains	125	5
Gross Unrealized Losses	(23)	(94)
Estimated Fair Value	115,890	75,910
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	38,547	50,413
Gross Unrealized Gains	27
Gross Unrealized Losses	(1)	(23)
Estimated Fair Value	38,573	50,390
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,500	4,000
Estimated Fair Value	$ 3,500	$ 4,000