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Stock Warrants (Details Textual) - USD ($) |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 15, 2018 | Oct. 10, 2018 | Oct. 10, 2014 | Nov. 18, 2016 | Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2018 | Oct. 31, 2018 | Dec. 31, 2017 | Dec. 26, 2017
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Warrants Not Settleable in Cash, Fair Value Disclosure |  |  |  |  |  |  |  |  |  | $ 9,000
Proceeds from Issuance of Common Stock |  |  |  |  |  |  | $ 12,200,000 |  |  |
Warrant liabilities |  |  |  |  | $ 0 | $ 90,000 | 0 |  | $ 4,083,000 |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | 13,672,173 |  |  |  |  |  |  |  |  |
Fair Value Adjustment of Warrants |  |  |  |  | $ 0 | (2,655,000) | $ (4,083,000) |  |  |
Conversion of Stock, Shares Converted |  |  |  |  | 7,598 |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ 1.38 |  |  |  |  |  |  | $ 1.38 |  |
Class A [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | 2,520,000 |  |  |  |  |  |  |  |  |
Class B [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | 15,723 |  |  |  |  |  |  |  |  |
Preferred Stock Conversion Price Per Share | $ 1.15 |  |  |  |  |  |  |  |  |
Series B Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | 13,672,173 |  |  |  |  |  |  |  |  |
Stock Issued During Period, Value, Issued for Services | $ 1,000 |  |  |  |  |  |  |  |  |
Preferred Stock, Par or Stated Value Per Share | $ 1,000 |  |  |  | $ 1,000 |  | $ 1,000 |  |  |
Conversion of Stock, Shares Converted | 13,672,173 |  |  |  |  |  |  |  |  |
IPO [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Warrants Not Settleable in Cash, Fair Value Disclosure |  |  |  | $ 15,700,000 | $ 100,000 | 1,300,000 |  |  |  |
Stock Issued During Period, Shares, New Issues |  |  |  | 714,286 |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights |  |  |  | 1,428,571 |  |  |  |  |  |
Fair Value Adjustment of Warrants |  |  |  |  |  | $ 2,300,000 |  |  |  |
Sale of Stock, Price Per Share |  |  | $ 1.47 | $ 35.00 |  |  |  |  |  |
IPO [Member] | Series A [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  | 50.05 |  |  |  |  |  |
IPO [Member] | Series B [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  | $ 60.20 |  |  |  |  |  |
Underwritten Public Offering [Member] | October 2018 Warrants [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Warrant Term | 5 years |  |  |  |  |  |  |  |  |
Over-Allotment Option [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Issuance Of Warrants To Purchase Of Common Stock | 1,807,826 |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues | 2,428,825 | 2,428,825 |  |  |  |  |  |  |  |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | 2,428,825 | 2,428,825 |  |  |  |  |  |  |  |
Stock Warrants [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Common Stock |  |  | $ 19,100,000 |  |  |  |  |  |  |
Sale of Stock, Number of Shares Issued in Transaction |  |  | 14,059,616 |  |  |  |  |  |  |
Issuance Of Warrants To Purchase Of Common Stock |  |  | 0.50 |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number |  |  | 61.25 |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Warrants Vested and Expected To Vest Outstanding Number |  |  | 200,852 |  |  |  |  |  |  |
Warrant liabilities |  |  |  |  | $ 0 |  |  |  |  |
Fair Value Adjustment of Warrants |  |  | $ 7,400,000 |  |  |  |  |  |  |
Warrant [Member] |  |  |  |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award Non Option Equity Instruments Warrants Exercisable Number |  |  |  |  |  |  |  |  |  | 714
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | 13,672,173 |  |  |  |  |  |  |  |  |

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- Definition The price per share at which the preferred stock of an entity that has priority over common stock in the distribution of dividends and in the event of liquidation of the entity can be converted. + References No definition available. + Details
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- Definition The value as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the share warrants plan. + References No definition available. + Details
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- Definition As of the balance sheet date, the number of warrants into which fully vested and expected to vest stock options outstanding can be converted under the option plan. + References No definition available. + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(i)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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