Significant Accounting Policies (Property and Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Retirement of property and equipment	$ 220,800	$ 25,800
Property and equipment, gross	1,097,574	1,184,593
Less: accumulated depreciation and amortization	(797,224)	(852,460)
Total property and equipment, net	$ 343,820	373,817
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	$ 190,887	271,461
Software
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Property and equipment, gross	$ 538,905	487,191
Equipment and furniture
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	7 years
Property and equipment, gross	$ 83,387	123,649
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 199,303	217,200
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	$ 15,883	14,097
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