Intangible assets and goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cost Basis [Abstract]
Intangible Assets, Beginning Balance	$ 151,400
Additions	667,000
Intangible Assets, Ending Balance	818,400	$ 151,400
Accumulated Amortization [Abstract]
Accumulated Amortization, Beginning Balance	(31,800)
Amortization	25,000,000	8,600,000	$ 7,000,000
Accumulated Amortization, Ending balance	(56,800)	(31,800)
Net book value of intangible assets	$ 761,600
Intangible assets, weighted average useful life	14 years 7 months 6 days
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
2019	$ 57,700
2020	57,600
2021	56,100
2022	53,400
2023 and beyond	536,800
Net book value of intangible assets	761,600
Goodwill, Cost Basis [Abstract]
Goodwill, Beginning Balance	49,100	41,000
Goodwill, Additions	210,600	8,100
Goodwill, Ending Balance	$ 259,700	$ 49,100	$ 41,000