Cash, Cash Equivalents and Investments - Additional Information (Detail)	12 Months Ended
Dec. 31, 2018 USD ($) Security	Dec. 31, 2017 USD ($) Security	Dec. 31, 2016 USD ($)
Cash And Cash Equivalents [Abstract]
Liquid investments with maturities	3 months
Cumulative unrealized loss, net of taxes	$ 15,000	$ 17,000	$ 30,000
Realized gains or losses	$ 0	$ 0	$ 0
Number of securities in unrealized loss position \| Security	0	15
Unrealized loss available for sale securities		$ 27,000
Unrealized loss available for sale securities fair value		$ 8,100,000
Municipal bonds maturity date	Jan. 31, 2019

The maturity date of the investment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

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- Definition

Available for sale securities in unrealized loss positions number of positions.

+ References

No definition available.

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- Definition

Cash and cash equivalents maximum maturity period.

+ References

No definition available.

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- Definition

Accumulated unrealized gain (loss), after tax, on 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 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669686-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e681-108580

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e637-108580

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- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

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- Definition

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

No definition available.

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