Other intangible assets (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net (excluding goodwill)	$ 16,318,000	$ 19,991,000	$ 17,129,000
Amortization of intangible assets	800,000	900,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2013	3,700,000
2014	3,500,000
2015	2,600,000
2016	2,200,000
2017	1,900,000
Thereafter	3,200,000
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	21,310,000	21,010,000	21,310,000
Finite-lived intangible assets, accumulated amortization	(12,211,000)	(10,197,000)	(11,701,000)
Intangible assets, net (excluding goodwill)	9,099,000	10,813,000	9,609,000
Noncompete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	7,236,000	7,086,000	7,236,000
Finite-lived intangible assets, accumulated amortization	(5,439,000)	(4,921,000)	(5,326,000)
Intangible assets, net (excluding goodwill)	1,797,000	2,165,000	1,910,000
Other intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	10,979,000	11,442,000	10,979,000
Finite-lived intangible assets, accumulated amortization	(5,557,000)	(4,429,000)	(5,369,000)
Intangible assets, net (excluding goodwill)	$ 5,422,000	$ 7,013,000	$ 5,610,000