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Basis of Presentation and New Accounting Standards (Details) $ / shares in Units, $ in Millions | May 23, 2018 $ / shares shares | Mar. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 $ / shares shares | May 24, 2018 shares | Dec. 31, 2017 $ / shares shares
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Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |
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
Common stock, shares authorized (in shares) | 75,000,000 | 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 | 6,200,000 | 115,651
Common stock, shares outstanding (in shares) | 61,600,000 | 438,116 | 296,609 | 6,200,000 | 115,651
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
Common stock, reverse stock split, fractional shares issued | 0 |  |  |  |
Operating lease, right-of-use asset | $ |  | $ 2.2 |  |  |
Operating lease, liability | $ |  | $ 2.2 |  |  |
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 |

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