Fair Value Measurements and Available for Sale Investments - Additional Information (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value hierarchy level 1 to level 2	$ 0	$ 0
Fair value hierarchy level 2 to level 1	0	0
Prepaid Expenses and Other Current Assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest and securities receivable	$ 11,200,000	$ 600,000

Interest and securities receivable.

No definition available.

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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.

+ Details

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- Definition

Amount of transfers of financial instruments classified in shareholders' equity 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
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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- Definition

Amount of transfers of financial instruments classified in shareholders' equity measured on a recurring basis out of level 2 of the fair value hierarchy into level 1.

+ References

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