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
Jun. 30, 2020
Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]    
Total Fair Value $ 346,501 $ 257,299
Fair Value, Measurements, Recurring    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 345,691 257,078
Total Unrealized Gain 819 233
Total Unrealized Loss (9) (12)
Total Fair Value 346,501 257,299
Fair Value, Measurements, Recurring | Money Market Funds | Level 1    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 54,181 63,554
Total Unrealized Gain 0 0
Total Unrealized Loss 0 0
Total Fair Value 54,181 63,554
Fair Value, Measurements, Recurring | U.S. Treasury Obligations | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 186,555 52,805
Total Unrealized Gain 202 46
Total Unrealized Loss (1) (1)
Total Fair Value 186,756 52,850
Fair Value, Measurements, Recurring | Government Agency Obligations | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 6,080 6,151
Total Unrealized Gain 9 1
Total Unrealized Loss 0 (1)
Total Fair Value 6,089 6,151
Fair Value, Measurements, Recurring | Corporate Debt Obligations | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 81,631 100,512
Total Unrealized Gain 599 180
Total Unrealized Loss (8) (10)
Total Fair Value 82,222 100,682
Fair Value, Measurements, Recurring | Commercial Paper | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 9,988 26,290
Total Unrealized Gain 0 0
Total Unrealized Loss 0 0
Total Fair Value 9,988 26,290
Fair Value, Measurements, Recurring | Asset-Backed Securities | Level 2    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 7,256 7,266
Total Unrealized Gain 9 6
Total Unrealized Loss 0  
Total Fair Value 7,265 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 (73,300) (72,507)
Total Unrealized Gain 0 0
Total Unrealized Loss 0 0
Total Fair Value (73,300) (72,507)
Fair Value, Measurements, Recurring | Amounts Classified As Short-Term Investments    
Schedule of Available-for-sale Securities [Line Items]    
Total Amortized Cost 272,391 184,571
Total Unrealized Gain 819 233
Total Unrealized Loss (9) (12)
Total Fair Value $ 273,201 $ 184,792