Goodwill and other intangible assets (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-lived intangible assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 10,815	$ 3,837
Amortization of intangible assets	1,200	2,000	$ 2,500
Estimated amortization expense for amortizable intangible assets
2019	1,856
2020	1,486
2021	1,096
2022	1,072
2023	1,006
Thereafter	4,299
Customer relationships [Member]
Finite-lived intangible assets [Line Items]
Intangible assets, gross	22,720	15,248
Intangible assets, less accumulated amortization	13,535	13,382
Intangible assets, net (excluding goodwill)	9,185	1,866
Noncompete agreements [Member]
Finite-lived intangible assets [Line Items]
Intangible assets, gross	2,605	2,430
Intangible assets, less accumulated amortization	1,956	1,805
Intangible assets, net (excluding goodwill)	649	625
Other [Member}
Finite-lived intangible assets [Line Items]
Intangible assets, gross	6,458	6,990
Intangible assets, less accumulated amortization	5,477	5,644
Intangible assets, net (excluding goodwill)	981	$ 1,346
Series of Individually Immaterial Business Acquisitions [Member]
Finite-lived intangible assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 8,200