Intangible assets - Costs and accumulated amortization (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Cost
Finite-Lived Intangible Assets, Gross	$ 9,890,000	$ 5,900,000
Accumulated amortization
Finite-Lived Intangible Assets, Accumulated Amortization	(4,850,000)	(4,008,333)
Intangible assets, net	5,040,000	1,891,667
Non-compete agreements
Cost
Finite-Lived Intangible Assets, Gross	530,000	400,000
Accumulated amortization
Finite-Lived Intangible Assets, Accumulated Amortization	(320,556)	(233,333)
Trade names
Cost
Finite-Lived Intangible Assets, Gross	2,700,000	1,400,000
Accumulated amortization
Finite-Lived Intangible Assets, Accumulated Amortization	(380,000)	(272,222)
Certifications/programs
Cost
Finite-Lived Intangible Assets, Gross	2,000,000	2,000,000
Accumulated amortization
Finite-Lived Intangible Assets, Accumulated Amortization	(2,000,000)	(1,944,444)
Customer backlogs
Cost
Finite-Lived Intangible Assets, Gross	460,000	100,000
Accumulated amortization
Finite-Lived Intangible Assets, Accumulated Amortization	(130,000)	(100,000)
Customer relationships
Cost
Finite-Lived Intangible Assets, Gross	2,000,000	2,000,000
Accumulated amortization
Finite-Lived Intangible Assets, Accumulated Amortization	(1,958,333)	$ (1,458,334)
Facility management contracts
Cost
Finite-Lived Intangible Assets, Gross	2,200,000
Accumulated amortization
Finite-Lived Intangible Assets, Accumulated Amortization	$ (61,111)