Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Impairment charges	$ 0	$ 0
Income tax penalties and interest expense	$ 0	0
Number of operating segments \| segment	1
Available-for-sale securities, cost basis	$ 29,900,000
Available-for-sale securities, fair value	29,900,000
Available-for-sale securities, unrealized loss	(3,000)
Accumulated other comprehensive loss	$ (3,000)	$ 0
Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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