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Available-for-Sale Investments - Summary of Available-for-Sale Securities Held (Detail) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost $ 100,777 $ 111,542
Gross unrealized gains 116 5
Gross unrealized losses (4) (70)
Fair Value 100,889 111,477
Commercial paper    
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost 20,484 53,549
Gross unrealized gains 18  
Gross unrealized losses (1) (47)
Fair Value 20,501 53,502
Corporate debt securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost 71,288 54,022
Gross unrealized gains 96 4
Gross unrealized losses (1) (23)
Fair Value 71,383 54,003
U.S. government agency securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost 9,005 3,971
Gross unrealized gains 2 1
Gross unrealized losses (2)  
Fair Value $ 9,005 $ 3,972