Annual report pursuant to Section 13 and 15(d)

Marketable Securities - Marketable Available-for-Sale Securities (Detail)

v3.21.1
Marketable Securities - Marketable Available-for-Sale Securities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]    
Estimated Fair Value $ 118,130 $ 166,076
Cash and Cash Equivalents [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 22,415 18,597
Estimated Fair Value 22,415 18,597
Cash and Cash Equivalents [Member] | Money Market Funds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 22,415 18,597
Estimated Fair Value 22,415 18,597
Short-term Investments [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 118,122 165,996
Gross Unrealized Gains 13 80
Gross Unrealized Losses (5)  
Estimated Fair Value 118,130 166,076
Short-term Investments [Member] | U.S. and Foreign Commercial Paper [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 38,561 51,102
Estimated Fair Value 38,561 51,102
Short-term Investments [Member] | U.S. and Foreign Corporate Debt Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 29,186 56,691
Gross Unrealized Gains 7 38
Gross Unrealized Losses (4)  
Estimated Fair Value 29,189 56,729
Short-term Investments [Member] | Asset-backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 7,883 39,756
Gross Unrealized Gains 2 33
Estimated Fair Value 7,885 39,789
Short-term Investments [Member] | U.S. Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 23,991 18,447
Gross Unrealized Gains 3 9
Estimated Fair Value 23,994 18,456
Short-term Investments [Member] | US Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 15,498  
Gross Unrealized Gains 1  
Estimated Fair Value 15,499  
Short-term Investments [Member] | Supranational Debt Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 3,003  
Gross Unrealized Losses (1)  
Estimated Fair Value 3,002  
Maketable Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 140,537 184,593
Gross Unrealized Gains 13 80
Gross Unrealized Losses (5)  
Estimated Fair Value $ 140,545 $ 184,673