Property and Equipment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property and Equipment
Property and equipment, gross	$ 110,086	$ 103,200
Less-Accumulated depreciation	(68,670)	(61,507)
Property and equipment, net	41,416	41,693
Depreciation expense	11,793	12,591	11,225
Land
Property and Equipment
Property and equipment, gross	2,404	2,282
Transportation equipment
Property and Equipment
Property and equipment, gross	38,352	34,590
Transportation equipment | Minimum
Property and Equipment
Estimated useful life	2 years
Transportation equipment | Maximum
Property and Equipment
Estimated useful life	10 years
Machinery and equipment
Property and Equipment
Property and equipment, gross	21,670	21,037
Machinery and equipment | Minimum
Property and Equipment
Estimated useful life	2 years
Machinery and equipment | Maximum
Property and Equipment
Estimated useful life	15 years
Computer and telephone equipment
Property and Equipment
Property and equipment, gross	18,481	17,329
Computer and telephone equipment | Minimum
Property and Equipment
Estimated useful life	2 years
Computer and telephone equipment | Maximum
Property and Equipment
Estimated useful life	10 years
Buildings and leasehold improvements
Property and Equipment
Property and equipment, gross	24,438	23,083
Buildings and leasehold improvements | Minimum
Property and Equipment
Estimated useful life	1 year
Buildings and leasehold improvements | Maximum
Property and Equipment
Estimated useful life	39 years
Furniture and fixtures
Property and Equipment
Property and equipment, gross	$ 4,741	$ 4,879
Furniture and fixtures | Minimum
Property and Equipment
Estimated useful life	3 years
Furniture and fixtures | Maximum
Property and Equipment
Estimated useful life	10 years