Summary of Held-to-Maturity Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 68,682	$ 68,624
Unrealized Gains		1
Unrealized Losses	(36)	(37)
Estimated Fair Value	68,646	68,588
Commercial Paper | Cash and Cash Equivalents
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	12,858	15,498
Unrealized Losses	(3)	(3)
Estimated Fair Value	12,855	15,495
Commercial Paper | Short Term Investments
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	50,203	46,978
Unrealized Losses	(32)	(33)
Estimated Fair Value	50,171	46,945
Corporate Bonds | Short Term Investments
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	5,621	6,148
Unrealized Gains		1
Unrealized Losses	(1)	(1)
Estimated Fair Value	$ 5,620	$ 6,148