Other intangible assets (Details 2) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 7,803,000	$ 9,166,000	$ 7,342,000
Amortization of intangible assets	600,000	700,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2016	2,500,000
2017	2,200,000
2018	1,200,000
2019	1,000,000
2020	500,000
Thereafter	1,000,000
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	17,145,000	20,975,000	20,975,000
Intangible assets, accumulated amortization	(12,680,000)	(15,649,000)	(16,845,000)
Intangible assets, net (excluding goodwill)	4,465,000	5,326,000	4,130,000
Noncompete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,430,000	4,409,000	4,409,000
Intangible assets, accumulated amortization	(1,548,000)	(3,504,000)	(3,655,000)
Intangible assets, net (excluding goodwill)	882,000	905,000	754,000
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	7,764,000	8,300,000	8,304,000
Intangible assets, accumulated amortization	(5,308,000)	(5,365,000)	(5,846,000)
Intangible assets, net (excluding goodwill)	$ 2,456,000	$ 2,935,000	$ 2,458,000