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Capital Stock - ATM Agreements - Additional Information (Details) - USD ($) |  | 1 Months Ended | 3 Months Ended
--- | --- | --- | ---
Dec. 18, 2018 | Dec. 31, 2018 | Feb. 28, 2017 | Mar. 31, 2019 | Mar. 31, 2018
Common Stock [Member] |  |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |  |
Sale of shares |  | 285,689 | 1,200,000 |  | 68,000
2018 ATM Agreement [Member] |  |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |  |
Sales commission paid per transaction (in hundredths) | 3.00% |  |  |  |
Maximum amount of shares can be issued | $ 30,000,000 |  |  |  |
2018 ATM Agreement [Member] | Common Stock [Member] |  |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |  |
Sale of shares |  |  |  | 0 |

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