Cash and Investments in Marketable Securities - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and Investments in Marketable Securities [Line Items]
Sales of investments	$ 0	$ 11,963,000	$ 37,549,000
Level 1 to level 2 transfers	0	0
Level 2 to level 1 transfers	0	0
Letter of credit	$ 6,800,000	$ 6,600,000
Maximum
Cash and Investments in Marketable Securities [Line Items]
Long term investment maturity period	2 years

Cash and Investments in Marketable Securities [Line Items]

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Long term investment maturity period.

+ References

No definition available.

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- Definition

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

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- Definition

Amount of cash inflow from sale 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

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-Publisher FASB
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-Topic 230
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 12
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