Marketable Securities Available-For-Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 243,784	$ 266,750
Gross Unrealized Gains	770	313
Gross Unrealized Losses	(10)	(6)
Fair Market Value	244,544	267,057
U.S. Treasury and government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	149,821	88,535
Gross Unrealized Gains	309	68
Gross Unrealized Losses	(10)	(2)
Fair Market Value	150,120	88,601
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	93,963	129,860
Gross Unrealized Gains	461	196
Gross Unrealized Losses	0	(1)
Fair Market Value	$ 94,424	130,055
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

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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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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