Significant Accounting Policies (Property and Equipment) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Total property and equipment, net	$ 367,779,000	$ 338,996,000
Retirement of property and equipment	11,400,000	10,300,000
Buildings
Property, Plant and Equipment [Line Items]
Property and equipment, gross	85,092,000	85,092,000
Estimated useful lives of property and equipment	40 years
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	237,709,000	204,110,000
Estimated useful lives of property and equipment	3 years
Software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	392,009,000	316,902,000
Estimated useful lives of property and equipment	3 years
Equipment and furniture
Property, Plant and Equipment [Line Items]
Property and equipment, gross	117,555,000	105,145,000
Estimated useful lives of property and equipment	7 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	211,625,000	168,990,000
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	10 years
Depreciable assets
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,043,990,000	880,239,000
Less accumulated depreciation and amortization	(722,691,000)	(597,268,000)
Assets under construction
Property, Plant and Equipment [Line Items]
Property and equipment, gross	18,893,000	28,438,000
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,587,000	27,587,000
Enterprise and Service Provider division
Property, Plant and Equipment [Line Items]
Asset Impairment Charges	$ 59,300,000