Quarterly report pursuant to Section 13 or 15(d)

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

v3.20.2
Financial Instruments - Summary of Estimated Fair Value and Related Valuation Input Hierarchy of Available-for-Sale Securities (Detail) - USD ($)
$ in Thousands
Sep. 30, 2020
Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value $ 326,848 $ 257,299
Fair Value, Measurements, Recurring    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 326,321 257,078
Total Unrealized Gain 535 233
Total Unrealized Loss (8) (12)
Total Fair Value 326,848 257,299
Fair Value, Measurements, Recurring | Money Market Funds | Level 1    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 55,707 63,554
Total Unrealized Gain 0 0
Total Unrealized Loss 0 0
Total Fair Value 55,707 63,554
Fair Value, Measurements, Recurring | U.S. Treasury Obligations | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 157,435 52,805
Total Unrealized Gain 151 46
Total Unrealized Loss 0 (1)
Total Fair Value 157,586 52,850
Fair Value, Measurements, Recurring | Government Agency Obligations | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 24,816 6,151
Total Unrealized Gain 13 1
Total Unrealized Loss (5) (1)
Total Fair Value 24,824 6,151
Fair Value, Measurements, Recurring | Corporate Debt Obligations | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 69,768 100,512
Total Unrealized Gain 361 180
Total Unrealized Loss (2) (10)
Total Fair Value 70,127 100,682
Fair Value, Measurements, Recurring | Commercial Paper | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 9,994 26,290
Total Unrealized Gain 0 0
Total Unrealized Loss 0 0
Total Fair Value 9,994 26,290
Fair Value, Measurements, Recurring | Asset-Backed Securities | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 8,601 7,266
Total Unrealized Gain 10 6
Total Unrealized Loss (1)  
Total Fair Value 8,610 7,272
Fair Value, Measurements, Recurring | Certificates 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 (62,283) (72,507)
Total Unrealized Gain 0 0
Total Unrealized Loss 0 0
Total Fair Value (62,283) (72,507)
Fair Value, Measurements, Recurring | Amounts Classified As Short-Term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 264,038 184,571
Total Unrealized Gain 535 233
Total Unrealized Loss (8) (12)
Total Fair Value $ 264,565 $ 184,792