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Retirement plan (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
United States |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer contributions to retirement plan | $ 43,866 | $ 31,308 | $ 33,422
Canada |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer contributions to retirement plan | $ 25,900 | $ 26,578 | $ 21,777

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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