Goodwill and intangible assets - Company's other intangible assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 33,783	$ 33,783
Accumulated amortization	8,487	7,771
Net	$ 25,296	26,012
Patents [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization Period (in years)	5 years
Gross Carrying Amount	$ 386	386
Accumulated amortization	385	383
Net	1	3
Covenant not to compete [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,270	1,270
Accumulated amortization	821	783
Net	$ 449	487
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	7,171	6,506
Net	$ 24,389	25,054
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	110	99
Net	$ 457	$ 468