| Retirement plans (Details) - USD ($) | 12 Months Ended | |
|---|---|---|
| Dec. 31, 2020 | Dec. 31, 2019 | |
| Retirement Benefits [Abstract] | ||
| Maximum employer annual contribution per employee, percent | 4.50% | |
| Contributions to plan | $ 124,507 | $ 265,280 | 
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- References No definition available. 
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- Definition Amount of cost for defined contribution plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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| X | ||||||||||
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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. No definition available. 
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