Other intangible assets (Details 2) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 5,347,000	$ 7,803,000	$ 5,925,000
Amortization of intangible assets	600,000	600,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2017	2,200,000
2018	1,200,000
2019	1,000,000
2020	500,000
2021	200,000
Thereafter	800,000
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	15,745,000	17,145,000	17,145,000
Intangible assets, less accumulated amortization	12,910,000	12,680,000	13,917,000
Intangible assets, net (excluding goodwill)	2,835,000	4,465,000	3,228,000
Noncompete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,430,000	2,430,000	2,430,000
Intangible assets, less accumulated amortization	1,695,000	1,548,000	1,658,000
Intangible assets, net (excluding goodwill)	735,000	882,000	772,000
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	7,086,000	7,764,000	7,768,000
Intangible assets, less accumulated amortization	5,309,000	5,308,000	5,843,000
Intangible assets, net (excluding goodwill)	$ 1,777,000	$ 2,456,000	$ 1,925,000