Property and Equipment (Schedule of Property and Equipment) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Computer and networking equipment	$ 655,043	$ 561,952
Purchased software	35,176	31,388
Furniture and fixtures	16,917	14,166
Office equipment	7,109	5,676
Leasehold improvements	44,539	36,358
Internal-use software	272,441	222,914
Property and equipment, gross	1,031,225	872,454
Accumulated depreciation and amortization	(686,134)	(579,411)
Property and equipment, net	$ 345,091	$ 293,043
Property, plant and equipment, estimated useful lives	1 year
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful lives	3 years
Software [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful lives	3 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful lives	5 years
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful lives	3 years
Minimum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful lives	2 years
Minimum [Member] | Internal-Use Software [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful lives	2 years
Maximum [Member] | Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful lives	12 years
Maximum [Member] | Internal-Use Software [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, estimated useful lives	3 years