Goodwill and intangible assets - Company's other intangible assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 33,783	$ 33,783
Accumulated amortization	11,331	10,633
Net	$ 22,452	23,150
Patents [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization Period (in years)	5 years
Gross Carrying Amount	$ 386	386
Accumulated amortization	386	386
Covenant not to compete [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,270	1,270
Accumulated amortization	958	937
Net	$ 312	333
Covenant not to compete [Member] | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization Period (in years)	10 years
Covenant not to compete [Member] | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization Period (in years)	6 years
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 31,560	31,560
Accumulated amortization	9,833	9,167
Net	$ 21,727	22,393
Customer relationships [Member] | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization Period (in years)	12 years
Customer relationships [Member] | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization Period (in years)	10 years
Above market leases [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization Period (in years)	13 years
Gross Carrying Amount	$ 567	567
Accumulated amortization	154	143
Net	$ 413	$ 424