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Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule Of Investments [Line Items]
Investments	$ 702,861	$ 725,227
Investments	77,365
Commercial paper
Schedule Of Investments [Line Items]
Investments	116,490	94,572
Corporate debt securities
Schedule Of Investments [Line Items]
Investments	419,293	544,978
Securities of government-sponsored entities
Schedule Of Investments [Line Items]
Investments	89,713	85,677
Restricted equity securities
Schedule Of Investments [Line Items]
Investments	$ 77,365	$ 0

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
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- Definition

Amount of restricted investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
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