Other intangible assets (Details 2) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 6,529,000	$ 7,908,000	$ 6,529,000	$ 7,908,000	$ 7,342,000
Amortization of intangible assets	600,000	600,000	1,900,000	2,000,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2016	2,500,000		2,500,000
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
Thereafter	1,000,000		1,000,000
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	17,145,000	20,975,000	17,145,000	20,975,000	20,975,000
Intangible assets, accumulated amortization	(13,524,000)	(16,455,000)	(13,524,000)	(16,455,000)	(16,845,000)
Intangible assets, net (excluding goodwill)	3,621,000	4,520,000	3,621,000	4,520,000	4,130,000
Noncompete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,430,000	4,409,000	2,430,000	4,409,000	4,409,000
Intangible assets, accumulated amortization	(1,622,000)	(3,632,000)	(1,622,000)	(3,632,000)	(3,655,000)
Intangible assets, net (excluding goodwill)	808,000	777,000	808,000	777,000	754,000
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	7,764,000	8,300,000	7,764,000	8,300,000	8,304,000
Intangible assets, accumulated amortization	(5,664,000)	(5,689,000)	(5,664,000)	(5,689,000)	(5,846,000)
Intangible assets, net (excluding goodwill)	$ 2,100,000	$ 2,611,000	$ 2,100,000	$ 2,611,000	$ 2,458,000