Short-term Investments - Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 117,159	$ 28,800
Gross unrealized gains	147	83
Gross unrealized losses	(2)	0
Fair value	117,304	28,883
Debt securities and equity securities, amortized cost	127,052
Debt and equity securities, unrealized gains	772
Debt securities and equity securities, unrealized losses	(2)
Debt and equity securities, fair value	127,822	28,883
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	78,243	22,338
Gross unrealized gains	89	71
Gross unrealized losses	(2)	0
Fair value	78,330	22,409
U.S. government-related debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	26,966	5,000
Gross unrealized gains	37	3
Gross unrealized losses	0	0
Fair value	27,003	5,003
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost	11,950	1,462
Gross unrealized gains	21	9
Gross unrealized losses	0	0
Fair value	11,971	$ 1,471
Corporate equity securities
Debt Securities, Available-for-sale [Line Items]
Equity securities, amortized cost	9,893
Equity securities, unrealized gain	625
Equity securities, gross unrealized losses	0
Equity securities, fair value	$ 10,518