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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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