Investments - Schedule of Fair Values of Available For Sale Debt Investments by Contractual Maturity (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Investments Debt And Equity Securities [Abstract]
Due in 1 year or less	$ 375,625
Due in 1 - 2 years	240,614
Due in 3 years	36,870
Instruments not due at a single maturity date	61,023
Total cash equivalents and investments	$ 714,132

Available for sale securities debt maturities after one through two years fair value.

No definition available.

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- Definition

Available for sale securities debt maturities within three year fair value.

+ References

No definition available.

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- Definition

Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), maturing in next fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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- Definition

Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), without single maturity date and not allocated over maturity grouping.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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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
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- References

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