Property and equipment, net (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 149,940,000	$ 148,820,000
Less accumulated depreciation	(95,260,000)	(91,063,000)
Property and equipment, net	54,680,000	57,757,000
Capital Leased Assets, Gross	3,000,000
Capital leases, amortization expense	400,000	200,000
Land [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,920,000	3,495,000
Building and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	20,421,000	21,286,000
Revenue Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	69,770,000	67,704,000
Service Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,847,000	27,456,000
Computers, Software and Related Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	28,737,000	28,524,000
Work In Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 245,000	$ 355,000