Fair Value Measurements - Narrative (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized cost of available-for-sale investments with maturities less than one year	$ 143,400,000	$ 135,600,000
Amortized cost of available-for-sale investments with maturities greater than one year	16,200,000	0
Net unrealized gains (losses) on investments, net of tax	70,000.00	(60,000.00)
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unrealized gain	0	0
Unrealized loss	$ 0	$ 0

Cash And Cash Equivalents, Accumulated Gross Unrealized Gain, Before Tax

No definition available.

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- Definition

Cash And Cash Equivalents, Accumulated Gross Unrealized Loss, Before Tax

+ References

No definition available.

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- Definition

Debt Securities, Available-For-Sale, Maturity, Allocated And Single Maturity Date, After One Year, Amortized Cost

+ References

No definition available.

+ Details

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- Definition

Amount, after tax, of accumulated unrealized gain (loss) 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://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e681-108580

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- Definition

Amortized cost of investment in debt security measured at fair value with change recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, 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
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27198-111563

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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