Common Stock - Narrative (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2019 USD ($) vote $ / shares shares	Dec. 31, 2018 USD ($) vote $ / shares shares	Dec. 17, 2018 $ / shares shares	Dec. 31, 2017 $ / shares shares
Class of Warrant or Right [Line Items]
Shares authorized (in shares)	29,879,220	29,879,220		29,879,220
Par value (in USD per share) \| $ / shares	$ 0.001	$ 0.001		$ 0.001
Shares issued (in shares)	1,386,615	1,135,310		663,270
Shares outstanding (in shares)	1,386,615	1,135,310		663,270
Dividends declared \| $	$ 0	$ 0
Number of votes entitled per share of common stock \| vote	1	1
Warrants to Purchase Common Stock
Class of Warrant or Right [Line Items]
Number of shares which may be purchased with warrants (in shares)		7,527	7,527
Warrant exercise price (in USD per share) \| $ / shares			$ 8.27
Warrants outstanding (in shares)	7,527	7,527

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Exercise price per share or per unit of warrants or rights outstanding.

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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.

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Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

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Number of warrants or rights outstanding.

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

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