Fair Value Measurements - Summary of Company's Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Investments, Amortized cost	$ 34,930	$ 26,761
Investments, Gross unrealized gains	862	1,350
Investments, Gross unrealized losses	(25)
Investments, Fair value	35,767	28,111
U.S. Treasuries [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	24,989
Trading securities, Gross unrealized losses	(25)
Trading securities, Fair value	24,964
Corporate Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost		19,081
Trading securities, Gross unrealized gains		141
Trading securities, Fair value		19,222
Mutual Funds Held In Rabbi Trust [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	9,941	7,680
Trading securities, Gross unrealized gains	862	1,209
Trading securities, Fair value	$ 10,803	$ 8,889