Marketable Securities - Available-For-Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Noncurrent investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 266,750
Gross Unrealized Gains	313
Gross Unrealized Losses	(6)
Fair Market Value	267,057
Noncurrent investments \| U.S. Treasury and government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	88,535
Gross Unrealized Gains	68
Gross Unrealized Losses	(2)
Fair Market Value	88,601
Noncurrent investments \| Corporate debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	129,860
Gross Unrealized Gains	196
Gross Unrealized Losses	(1)
Fair Market Value	130,055
Noncurrent investments \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	48,355
Gross Unrealized Gains	49
Gross Unrealized Losses	(3)
Fair Market Value	$ 48,401
Current investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 196,361
Gross Unrealized Gains		50
Gross Unrealized Losses		(56)
Fair Market Value		196,355
Current investments \| U.S. Treasury and government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		69,275
Gross Unrealized Gains		12
Gross Unrealized Losses		(17)
Fair Market Value		69,270
Current investments \| Corporate debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		105,897
Gross Unrealized Gains		38
Gross Unrealized Losses		(25)
Fair Market Value		105,910
Current investments \| Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		21,189
Gross Unrealized Gains		0
Gross Unrealized Losses		(14)
Fair Market Value		$ 21,175

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-SubTopic 10
-Section 50
-Paragraph 2
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
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