Significant Accounting Policies (Property and Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Retirement of property and equipment	$ 25,800	$ 11,400
Property and equipment, gross	1,184,593	1,043,990
Less accumulated depreciation and amortization	(852,460)	(722,691)
Total property and equipment, net	$ 373,817	367,779
Buildings
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	40 years
Property and equipment, gross	$ 85,092	85,092
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Property and equipment, gross	$ 271,461	237,709
Software
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Property and equipment, gross	$ 487,191	392,009
Equipment and furniture
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	7 years
Property and equipment, gross	$ 123,649	117,555
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 217,200	211,625
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	10 years
Assets under construction
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 14,097	18,893
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,587	27,587
Enterprise and Service Provider
Property, Plant and Equipment [Line Items]
Asset Impairment Charges	$ 123,000	$ 59,300