Other intangible assets (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Net (Excluding Goodwill)	$ 19,991,000	$ 24,351,000	$ 20,843,000
Amortization of Intangible Assets	900,000	900,000
Estimated amortization expense for amortizable intangible assets [Abstract]
2012	3,800,000
2013	3,700,000
2014	3,300,000
2015	2,600,000
2016	2,200,000
Thereafter	5,300,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	21,010,000	21,702,000	21,702,000
Finite-Lived Intangible Assets, Accumulated Amortization	(10,197,000)	(8,890,000)	(10,392,000)
Intangible Assets, Net (Excluding Goodwill)	10,813,000	12,812,000	11,310,000
Noncompete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	7,086,000	7,685,000	7,685,000
Finite-Lived Intangible Assets, Accumulated Amortization	(4,921,000)	(4,898,000)	(5,371,000)
Intangible Assets, Net (Excluding Goodwill)	2,165,000	2,787,000	2,314,000
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	11,442,000	12,899,000	11,442,000
Finite-Lived Intangible Assets, Accumulated Amortization	(4,429,000)	(4,147,000)	(4,223,000)
Intangible Assets, Net (Excluding Goodwill)	$ 7,013,000	$ 8,752,000	$ 7,219,000