Available-for-Sale Marketable Securities - Summary of Available-for-Sale Marketable Securities by Major Type of Security (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 95,444	$ 199,690
Gross Unrealized Gains	638	197
Gross Unrealized Losses	(3)	(27)
Estimated Fair Value	96,079	199,860
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,070	16,052
Gross Unrealized Gains	180	31
Gross Unrealized Losses		(2)
Estimated Fair Value	13,250	16,081
U.S. Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,499	25,803
Gross Unrealized Gains	18	14
Gross Unrealized Losses		(1)
Estimated Fair Value	3,517	25,816
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	62,077	115,788
Gross Unrealized Gains	416	125
Gross Unrealized Losses	(3)	(23)
Estimated Fair Value	62,490	115,890
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,298	38,547
Gross Unrealized Gains	24	27
Gross Unrealized Losses		(1)
Estimated Fair Value	13,322	38,573
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,500	3,500
Estimated Fair Value	$ 3,500	$ 3,500