Cash Equivalents, Restricted Cash and Investments - Amortized Cost and Fair Value of Cash Equivalents and Investments 2 (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Abstract]
Cash equivalents	$ 72,699	$ 30,139
Short-term investments	235,399	404,273
Long-term investments	90,028	23,800
Total available-for-sale securities	$ 398,126	$ 458,212