Annual report pursuant to Section 13 and 15(d)

Financial Instruments - Summary of Estimated Fair Value and Related Valuation Input Hierarchy of Available-for-Sale Securities (Detail)

v3.20.4
Financial Instruments - Summary of Estimated Fair Value and Related Valuation Input Hierarchy of Available-for-Sale Securities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value $ 499,345 $ 257,299
Fair Value, Measurements, Recurring    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 499,049 257,078
Total Unrealized Gain 311 233
Total Unrealized Loss (15) (12)
Total Fair Value 499,345 257,299
Fair Value, Measurements, Recurring | Money Market Funds | Level 1    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 168,343 63,554
Total Unrealized Gain 0 0
Total Unrealized Loss 0 0
Total Fair Value 168,343 63,554
Fair Value, Measurements, Recurring | U.S. Treasury Obligations | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 230,239 52,805
Total Unrealized Gain 113 46
Total Unrealized Loss (6) (1)
Total Fair Value 230,346 52,850
Fair Value, Measurements, Recurring | Government Agency Obligations | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 22,537 6,151
Total Unrealized Gain 22 1
Total Unrealized Loss (3) (1)
Total Fair Value 22,556 6,151
Fair Value, Measurements, Recurring | Corporate Debt Obligations | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 50,080 100,512
Total Unrealized Gain 166 180
Total Unrealized Loss (1) (10)
Total Fair Value 50,245 100,682
Fair Value, Measurements, Recurring | Commercial Paper | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 17,990 26,290
Total Unrealized Gain 0 0
Total Unrealized Loss 0 0
Total Fair Value 17,990 26,290
Fair Value, Measurements, Recurring | Asset-Backed Securities | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 9,860 7,266
Total Unrealized Gain 10 6
Total Unrealized Loss (5) 0
Total Fair Value 9,865 7,272
Fair Value, Measurements, Recurring | Certificate of Deposit | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost   500
Total Unrealized Gain   0
Total Unrealized Loss   0
Total Fair Value   500
Fair Value, Measurements, Recurring | Amounts Classified As Cash Equivalents    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 199,090 72,507
Total Unrealized Gain 0 0
Total Unrealized Loss 0 0
Total Fair Value 199,090 72,507
Fair Value, Measurements, Recurring | Amounts Classified As Short-Term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 299,959 184,571
Total Unrealized Gain 311 233
Total Unrealized Loss (15) (12)
Total Fair Value $ 300,255 $ 184,792