Quarterly report pursuant to Section 13 or 15(d)

Investments in Marketable Securities - Schedule of Amortized Cost and Fair Value of Marketable Securities, Available-for-Sale, by Type of Security (Detail)

v3.20.2
Investments in Marketable Securities - Schedule of Amortized Cost and Fair Value of Marketable Securities, Available-for-Sale, by Type of Security (Detail) - USD ($)
$ in Thousands
Sep. 30, 2020
Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 213,485 $ 209,985
Allowance for Credit Losses 0  
Fair Value 216,018 211,561
Short-term investments [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 169,239 150,517
Allowance for Credit Losses 0  
Gross Unrealized Gains 275 240
Gross Unrealized Losses (1) (5)
Fair Value 169,513 150,752
Short-term investments [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 93,425 124,389
Allowance for Credit Losses 0  
Gross Unrealized Gains 216 196
Gross Unrealized Losses 0 (5)
Fair Value 93,641 124,580
Short-term investments [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 37,721 0
Allowance for Credit Losses 0  
Gross Unrealized Gains 19 0
Gross Unrealized Losses 0 0
Fair Value 37,740 0
Short-term investments [Member] | Corporate debt [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 38,093 26,128
Allowance for Credit Losses 0  
Gross Unrealized Gains 40 44
Gross Unrealized Losses (1) 0
Fair Value 38,132 26,172
Long-term marketable securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 44,246 59,468
Allowance for Credit Losses 0  
Gross Unrealized Gains 2,355 1,358
Gross Unrealized Losses (96) (17)
Fair Value 46,505 60,809
Long-term marketable securities [Member] | U.S. Treasuries [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 3,396 24,188
Allowance for Credit Losses 0  
Gross Unrealized Gains 293 235
Gross Unrealized Losses 0 0
Fair Value 3,689 24,423
Long-term marketable securities [Member] | U.S. Government Sponsored Entities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,233 1,353
Allowance for Credit Losses 0  
Gross Unrealized Gains 36 3
Gross Unrealized Losses 0 (1)
Fair Value 1,269 1,355
Long-term marketable securities [Member] | Corporate debt [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 32,584 25,447
Allowance for Credit Losses 0  
Gross Unrealized Gains 1,837 1,027
Gross Unrealized Losses (64) (3)
Fair Value 34,357 26,471
Long-term marketable securities [Member] | ABS and other [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 7,033 8,480
Allowance for Credit Losses 0  
Gross Unrealized Gains 189 93
Gross Unrealized Losses (32) (13)
Fair Value $ 7,190 $ 8,560