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Stockholders' Equity - Summary of 2001 Plan for Restricted Stock Grants (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Total compensation cost attributable to shares awarded | $ 3,100,000 | $ 2,800,000 | $ 1,800,000
Restricted Stock |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares awarded (in shares) | 44,424 | 36,799 | 59,240
Average grant-date market price per share (in usd per share) | $ 11.48 | $ 9.60 | $ 4.22
Total compensation cost attributable to shares awarded | $ 509,988 | $ 353,000 | $ 250,000
Compensation cost recognized related to current and prior year awards | $ 518,164 | $ 283,307 | $ 249,995
Restricted Stock | Non Employee Director |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares awarded (in shares) | 7,404 | 5,257 | 11,848
Total compensation cost attributable to shares awarded | $ 63,745 |  |
Restricted Stock | Additional Non-employee Director |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Shares awarded (in shares) | 4,866 |  |
Average grant-date market price per share (in usd per share) | $ 13.10 |  |

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