| Intangible assets other than goodwill - Schedule of Estimated Future Amortization Expense (Details) - USD ($) | Dec. 31, 2018 | Dec. 31, 2017 | 
|---|---|---|
| Finite-Lived Intangible Assets [Line Items] | ||
| Intangible assets, net | $ 2,893,990 | $ 2,896,458 | 
| Contract Asset and Liability | ||
| Finite-Lived Intangible Assets [Line Items] | ||
| 2019 | 458,593 | |
| 2020 | 437,329 | |
| 2021 | 468,273 | |
| 2022 | 449,717 | |
| 2023 | 380,130 | |
| Thereafter | 1,227,320 | |
| Intangible assets, net | 3,421,362 | |
| Contract Asset and Liability | Contract related intangibles | ||
| Finite-Lived Intangible Assets [Line Items] | ||
| 2019 | 705,430 | |
| 2020 | 675,232 | |
| 2021 | 680,719 | |
| 2022 | 655,086 | |
| 2023 | 578,426 | |
| Thereafter | 1,668,066 | |
| Intangible assets, net | 4,962,959 | |
| Contract Asset and Liability | Non-contract related intangibles | ||
| Finite-Lived Intangible Assets [Line Items] | ||
| 2019 | 246,837 | |
| 2020 | 237,903 | |
| 2021 | 212,446 | |
| 2022 | 205,369 | |
| 2023 | 198,296 | |
| Thereafter | 440,746 | |
| Intangible assets, net | $ 1,541,597 | 
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- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. No definition available. 
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- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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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. No definition available. 
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- Definition Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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