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Marketable Securities Available-For-Sale Marketable Securities (Detail) - Noncurrent Investments - USD ($)
$ in Thousands
Mar. 31, 2020
Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost $ 246,364 $ 266,750
Gross Unrealized Gains 1,186 313
Gross Unrealized Losses (174) (6)
Fair Market Value 247,376 267,057
U.S. Treasury and government agencies    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 87,014 88,535
Gross Unrealized Gains 558 68
Gross Unrealized Losses 0 (2)
Fair Market Value 87,572 88,601
Corporate debt    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 122,964 129,860
Gross Unrealized Gains 572 196
Gross Unrealized Losses (110) (1)
Fair Market Value 123,426 130,055
Asset-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 36,386 48,355
Gross Unrealized Gains 56 49
Gross Unrealized Losses (64) (3)
Fair Market Value $ 36,378 $ 48,401