Cash Equivalents and Investments - Schedule of Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available-for-sale [Line Items]
Available-for-sale Securities	$ 81,574	$ 74,510
Corporate Securities [Member]
Available-for-sale [Line Items]
Available-for-sale Securities	56,680	32,962
Municipal Debt Securities [Member]
Available-for-sale [Line Items]
Available-for-sale Securities	13,523	29,066
Federal Home Loan Securities [Member]
Available-for-sale [Line Items]
Available-for-sale Securities	6,529	8,013
Certificates of Deposit [Member]
Available-for-sale [Line Items]
Available-for-sale Securities	$ 4,842	$ 4,469