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Capital Stock - ATM Agreements - Additional Information (Details) - USD ($) | 1 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Feb. 28, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Nov. 12, 2015
Class Of Warrant Or Right [Line Items] |  |  |  |
Proceeds from issuance of common stock |  | $ 2,331,000 | $ 5,400,000 |
Common Stock [Member] |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |
Sale of shares | 1,200,000 |  |  |
2015 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 |  |  |  | $ 75,000,000
Proceeds from issuance of common stock |  | $ 2,400,000 | 600,000 |
Offering costs offset against proceeds upon sale of common stock |  | $ 100,000 | $ 200,000 |
Agreement expired date |  | 2018-02 |  |
2015 ATM Agreement [Member] | Common Stock [Member] |  |  |  |
Class Of Warrant Or Right [Line Items] |  |  |  |
Sale of shares |  | 67,658 | 110,252 |

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