Summary of Significant Accounting Policies (Details 5) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Property and Equipment
Depreciation expense	$ 47,900,000	$ 43,900,000	$ 37,800,000
Property and equipment, gross	380,101,000	341,971,000
Accumulated depreciation	(262,079,000)	(230,157,000)
Property and equipment, net	118,022,000	111,814,000
Buildings and improvements
Property and Equipment
Estimated useful lives of assets, minimum (in years)	2
Estimated useful lives of assets, maximum (in years)	10
Property and equipment, gross	5,037,000	5,321,000
Equipment
Property and Equipment
Estimated useful lives of assets, minimum (in years)	3
Estimated useful lives of assets, maximum (in years)	15
Property and equipment, gross	150,874,000	141,427,000
Capitalized internal-use software
Property and Equipment
Estimated useful lives of assets, minimum (in years)	3
Estimated useful lives of assets, maximum (in years)	5
Depreciation expense	28,900,000	26,600,000	20,200,000
Property and equipment, gross	224,190,000	195,223,000
Property and equipment, net	$ 62,000,000	$ 61,900,000