Financial Instruments - Fair Value and Gross Unrealized Losses Related to Individual Available-for-Sale Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 66,125	$ 20,031
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Losses	(46)	(10)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or more, Fair Value		8,753
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or more, Gross Unrealized Losses		(3)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	66,125	28,784
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses	(46)	(13)
Corporate bonds and notes
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	53,137	20,031
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Losses	(42)	(10)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or more, Fair Value		8,753
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or more, Gross Unrealized Losses		(3)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	53,137	28,784
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses	(42)	$ (13)
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	12,988
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Gross Unrealized Losses	(4)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	12,988
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses	$ (4)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
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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), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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