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Cash Equivalents and Investments - Schedule of Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Short-Term	$ 9,902	$ 10,292
Long-Term	90,186	80,682
Municipal Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Short-Term	8,432	8,312
Long-Term	48,613	46,195
Federal Home Loan Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Short-Term		1,000
Long-Term	36,393	30,322
Certificates of Deposit [Member]
Schedule of Held-to-maturity Securities [Line Items]
Short-Term	1,470	980
Long-Term	$ 5,180	$ 4,165

X

- Definition

Amount of investment in debt security measured at amortized cost (held-to-maturity), classified as current.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26626-111562

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- Definition

Amount of investment in debt security measured at amortized cost (held-to-maturity), classified as noncurrent.

+ References

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