Other intangible assets (Details 2) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 3,465,000	$ 5,347,000	$ 3,837,000
Amortization of intangible assets	400,000	600,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2018	1,300,000
2019	1,000,000.0
2020	500,000
2021	300,000
2022	300,000
Thereafter	500,000
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,668,000	15,745,000	15,248,000
Intangible assets, less accumulated amortization	13,007,000	12,910,000	13,382,000
Intangible assets, net (excluding goodwill)	1,661,000	2,835,000	1,866,000
Noncompete agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,430,000	2,430,000	2,430,000
Intangible assets, less accumulated amortization	1,842,000	1,695,000	1,805,000
Intangible assets, net (excluding goodwill)	588,000	735,000	625,000
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	6,458,000	7,086,000	6,990,000
Intangible assets, less accumulated amortization	5,242,000	5,309,000	5,644,000
Intangible assets, net (excluding goodwill)	$ 1,216,000	$ 1,777,000	$ 1,346,000