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Fair Value Measurements - Estimated Fair Value of Equity Securities Assumptions (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 $ / shares | Dec. 31, 2018
Closing Common Stock Price [Member] | OTC exchange [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input, Closing common stock price | $ 0.20 |
Discount for Lack of Marketability [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input |  | 35
Discount for Lack of Marketability [Member] | Tranche 1 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input | 24 |
Discount for Lack of Marketability [Member] | Tranche 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input | 35 |
Liquidity of Shares [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input term |  | 1 year 5 months 12 days
Liquidity of Shares [Member] | Tranche 1 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input term | 1 year |
Liquidity of Shares [Member] | Tranche 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input term | 2 years |
Liquidation [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input |  | 20
Near-term Sale [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input |  | 5
Near-term Financing [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |
Valuation assumptions, measurement input |  | 75

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