Other intangible assets (Details 2) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 4,785,000	$ 7,160,000	$ 4,785,000	$ 7,160,000	$ 5,925,000
Amortization of intangible assets	600,000	600,000	1,200,000	1,300,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2017	2,200,000		2,200,000
2018	1,200,000		1,200,000
2019	1,000,000		1,000,000
2020	500,000		500,000
2021	200,000		200,000
Thereafter	800,000		800,000
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	15,745,000	17,145,000	15,745,000	17,145,000	17,145,000
Intangible assets, less accumulated amortization	13,302,000	13,108,000	13,302,000	13,108,000	13,917,000
Intangible assets, net (excluding goodwill)	2,443,000	4,037,000	2,443,000	4,037,000	3,228,000
Noncompete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,430,000	2,430,000	2,430,000	2,430,000	2,430,000
Intangible assets, less accumulated amortization	1,732,000	1,585,000	1,732,000	1,585,000	1,658,000
Intangible assets, net (excluding goodwill)	698,000	845,000	698,000	845,000	772,000
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	7,086,000	7,764,000	7,086,000	7,764,000	7,768,000
Intangible assets, less accumulated amortization	5,442,000	5,486,000	5,442,000	5,486,000	5,843,000
Intangible assets, net (excluding goodwill)	$ 1,644,000	$ 2,278,000	$ 1,644,000	$ 2,278,000	$ 1,925,000