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Organization and Operations - Additional Information (Details) |  |  |  |  |  |  |  |  |  |  |  |  | 3 Months Ended | 7 Months Ended | 10 Months Ended | 12 Months Ended |  |  |
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Aug. 05, 2019 $ / shares shares | Apr. 25, 2019 USD ($) | Apr. 24, 2019 USD ($) | Sep. 21, 2018 USD ($) | Aug. 28, 2018 $ / shares | Jul. 25, 2018 USD ($) $ / shares shares | Jun. 01, 2018 USD ($) | May 23, 2018 $ / shares shares | Nov. 28, 2017 USD ($) $ / shares shares | Sep. 05, 2017 $ / shares | May 31, 2017 USD ($) $ / shares shares | Apr. 11, 2017 USD ($) $ / shares shares | Mar. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) $ / shares shares | Mar. 31, 2018 USD ($) shares | Dec. 31, 2018 USD ($) $ / shares shares | Mar. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) Subsidiary $ / shares shares | Dec. 31, 2017 USD ($) $ / shares shares | May 24, 2018 shares | Nov. 27, 2017 shares | Dec. 31, 2016 USD ($) shares
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of wholly-owned subsidiaries | Subsidiary |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 |  |  |  |
Reverse stock split of common stock |  |  |  |  |  |  |  | 0.1 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares |  |  |  |  |  |  |  | $ 0.001 |  |  |  |  | $ 0.001 | $ 0.001 |  | $ 0.001 | $ 0.001 | $ 0.001 | $ 0.001 |  |  |
Common stock, shares authorized (in shares) |  |  |  |  |  |  |  | 75,000,000 |  |  |  |  | 100,000,000 | 100,000,000 |  | 100,000,000 | 100,000,000 | 100,000,000 | 100,000,000 | 100,000,000 |  |
Common stock, shares issued (in shares) |  |  |  |  |  |  |  | 61,600,000 |  |  |  |  | 438,116 | 296,609 |  | 296,609 | 438,116 | 296,609 | 115,651 | 6,200,000 |  |
Common stock, shares outstanding (in shares) |  |  |  |  |  |  |  | 61,600,000 |  |  |  |  | 438,116 | 296,609 |  | 296,609 | 438,116 | 296,609 | 115,651 | 6,200,000 |  |
Number of shares callable by warrants (in shares) |  |  |  |  |  |  |  | 23,400,000 |  |  |  |  |  |  |  |  |  |  |  | 2,300,000 |  |
Preferred stock, shares authorized (in shares) |  |  |  |  |  |  |  | 5,000,000 |  |  |  |  | 5,000,000 | 5,000,000 |  | 5,000,000 | 5,000,000 | 5,000,000 | 5,000,000 | 5,000,000 |  |
Common stock, reverse stock split, fractional shares issued |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net loss | $ |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,150,000 |  | $ 4,409,000 |  |  | $ 12,634,000 | $ 22,686,000 |  |  |
Net loss from discountinued operations | $ |  |  |  |  |  |  |  |  |  |  |  |  | 686,000 |  | 1,130,000 |  |  | 3,756,000 | 9,592,000 |  |  |
Accumulated deficit | $ |  |  |  |  |  |  |  |  |  |  |  |  | (417,533,000) | $ (414,383,000) |  | $ (414,383,000) | $ (417,533,000) | (414,383,000) | (401,749,000) |  |  |
Net cash used in operating activities | $ |  |  |  |  |  |  |  |  |  |  |  |  | $ (3,270,000) |  | (4,119,000) |  |  | $ (11,975,000) | (18,128,000) |  |  |
Substantial doubt about going concern, description |  |  |  |  |  |  |  |  |  |  |  |  | These factors raise substantial doubt about the Company’s ability to continue as a going concern. |  |  |  |  | These factors raise substantial doubt about the Company’s ability to continue as a going concern |  |  |  |
Net proceeds excess receives from unrestricted cash | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,000,000 |  |  |  |
Cash and cash equivalents | $ |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,872,000 | 5,261,000 |  | 5,261,000 | 3,872,000 | 5,261,000 | 9,550,000 |  |  | $ 12,600,000
Minimum cash/cash equivalents covenant | $ |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 | $ 2,000,000 |  | $ 2,000,000 | $ 2,000,000 | 2,000,000 |  |  |  |
Common stock issued (in shares) |  |  |  |  |  | 6,723 |  |  | 10,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock, net | $ |  |  |  |  |  |  |  |  |  |  |  |  | 1,919,000 |  | (150,000) |  |  | 0 | 0 |  |  |
Proceeds from issuance warrants | $ |  |  |  |  |  | $ 5,700,000 |  |  | $ 8,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Date from which warrants are exercisable |  |  |  |  |  |  |  |  | May 18, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued, value | $ |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,873,000 |  | $ 27,000 |  |  | 1,624,000 | 12,716,000 |  |  |
Series B Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  |  |  |  |  |  | 360,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares authorized (in shares) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10,000 |
Common stock issued (in shares) |  |  |  |  |  |  |  |  | 60,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued, value | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 8,767,000 |  |  |
Series C Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  |  |  | 7,059,150 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares authorized (in shares) |  |  |  |  |  | 7,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of convertible shares converted into common stock (in shares) |  |  |  |  |  | 168,478 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued, value | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,041,000 |  |  |  |
Nasdaq Stock Market LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of consecutive business days no longer able to meet the required closing bid price of common stock |  |  |  |  | 30 days |  |  |  |  | 30 days |  |  |  |  |  |  |  |  |  |  |  |
Minimum bid price of common stock required for Nasdaq listing rule | $ / shares |  |  |  |  | $ 1.00 |  |  |  |  | $ 1.00 |  |  |  |  |  |  |  |  |  |  |  |
Grace period provided with minimum bid price for Nasdaq listing rule |  |  |  |  | 180 days |  |  |  |  | 180 days |  |  |  |  |  |  |  |  |  |  |  |
Grace date for minimum bid price requirement for Nasdaq listing |  |  |  |  | Feb. 25, 2019 |  |  |  |  | Mar. 05, 2018 |  |  |  |  |  |  |  |  |  |  |  |
Common stock minimum bid price required to regain compliance | $ / shares |  |  |  |  | $ 1.00 |  |  |  |  | $ 1.00 |  |  |  |  |  |  |  |  |  |  |  |
Number of consecutive business days required to regain compliance |  |  |  |  | 10 days |  |  |  |  | 10 days |  |  |  |  |  |  |  |  |  |  |  |
Additional grace period provided with minimum bid price to regain compliance |  |  |  |  | 180 days |  |  |  |  | 180 days |  |  |  |  |  |  |  |  |  |  |  |
Date to regain compliance after meeting continued listing requirement |  |  |  |  | Aug. 26, 2019 |  |  |  |  | Sep. 04, 2018 |  |  |  |  |  |  |  |  |  |  |  |
Description of compliance with minimum bid price requirement |  |  |  |  | We were granted an additional compliance period of 180 calendar days, or until August 26, 2019, in which to regain compliance after meeting the continued listing requirement for market value of publicly held shares and all other initial listing standards for the Nasdaq Capital Market, with the exception of the bid price requirement, and providing notice to Nasdaq staff of our intent to cure the deficiency during this second compliance period, by effecting a reverse stock split, if necessary. |  |  |  |  |  |  |  |  |  |  |  |  | We were granted an additional compliance period of 180 calendar days, or until August 26, 2019, in which to regain compliance after meeting the continued listing requirement for market value of publicly held shares and all other initial listing standards for the Nasdaq Capital Market, with the exception of the bid price requirement, and providing notice to Nasdaq staff of our intent to cure the deficiency during this second compliance period, by effecting a reverse stock split, if necessary. |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, shares outstanding (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 438,116 | 296,609 | 123,227 | 296,609 | 438,116 | 296,609 | 115,651 |  |  | 43,416
Number of shares callable by warrants (in shares) |  |  |  |  |  | 50 |  |  | 36,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  | 6,723 |  |  | 10,000 |  |  |  | 139,855 |  | 201 |  |  | 92,169 | 24,474 |  |  |
Share issued, price per share | $ / shares |  |  |  |  |  |  |  |  |  |  |  | $ 550.00 |  |  |  |  |  |  |  |  |  |
Warrant exercise price (in dollars per share) | $ / shares |  |  |  |  |  | $ 39.93 |  |  | $ 166.65 |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | B. Riley FBR [Member] | Sales Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,584 | 200,000 |  |  |  |  |
Proceeds from sale of common stock, net | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,700,000 | $ 3,800,000 |  |  |  |  |
Common Stock [Member] | Lincoln Park [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 12,802 |  |  |  |  |  |  |  |
Proceeds from sale of common stock, net | $ |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 300,000 |  |  |  |  |  |  |  |
Common stock issued, value | $ |  |  |  | $ 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period exercisable from the date of issuance |  |  |  | 24 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Series B Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of convertible shares converted into common stock (in shares) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7,375 |  |  | 7,921 | 45,413 |  |  |
Common Stock [Member] | Series C Convertible Preferred Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of convertible shares converted into common stock (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 1,652 |  |  |  |  | 80,868 |  |  |  |
Common Stock [Member] | Maxim Group LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  |  | 1,698 | 17,881 |  |  |  |  |  |  |  |  |  |
Share issued, price per share | $ / shares |  |  |  |  |  |  |  |  |  |  | $ 550.00 | $ 520.00 |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock, net | $ |  |  |  |  |  |  |  |  |  |  | $ 800,000 | $ 8,700,000 |  |  |  |  |  |  |  |  |  |
Closing of offering date |  |  |  |  |  |  |  |  |  |  |  | Apr. 17, 2017 |  |  |  |  |  |  |  |  |  |
Number of days granted as option to purchase additional shares of common stock to underwriter |  |  |  |  |  |  |  |  |  |  |  | 45 days |  |  |  |  |  |  |  |  |  |
Additional shares of common stock |  |  |  |  |  |  |  |  |  |  |  | 1,888 |  |  |  |  |  |  |  |  |  |
Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrestricted cash and cash equivalents | $ |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,000,000 | $ 2,000,000 |  | $ 2,000,000 | $ 2,000,000 | $ 2,000,000 |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrestricted gross cash proceeds required to extend interest-only period | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7,500,000 |  |  |  |
Maximum [Member] | Common Stock [Member] | B. Riley FBR [Member] | Sales Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock, net | $ |  |  |  |  |  |  | $ 6,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2014 Equity Incentive Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares callable by warrants (in shares) |  |  |  |  |  |  |  | 9,100,000 |  |  |  |  |  |  |  |  |  |  |  | 900,000 |  |
Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse stock split of common stock | 0.02 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares | $ 0.001 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock, shares authorized (in shares) | 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, reverse stock split, fractional shares issued | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse stock split of common stock description | Upon effectiveness, each 50 shares of issued and outstanding Common Stock were converted into one newly issued and outstanding share of Common Stock. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reverse Stock Split Effective Date For Trading Purposes | Aug. 06, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of UK Subsidiary and Certain Assets [Member] | Loan and Security Agreement [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash proceeds from sale of subsidiary | $ |  |  | $ 4,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments for principal, interest and fees | $ |  |  | $ 1,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of the Japanese Subsidiary and Certain Assets [Member] | Loan and Security Agreement [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash proceeds from sale of subsidiary | $ |  | $ 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments for principal, interest and fees | $ |  | $ 1,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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