Property and Equipment (Schedule of Property and Equipment) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 years	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Computer and networking equipment	$ 561,952	$ 492,685
Purchased software	31,388	29,885
Furniture and fixtures	14,166	12,770
Office equipment	5,676	4,792
Leasehold improvements	36,358	29,914
Internal-use software	222,914	177,918
Property and equipment, gross	872,454	747,964
Accumulated depreciation and amortization	(579,411)	(492,035)
Property and equipment, net	$ 293,043	$ 255,929
Property, plant and equipment, useful life, minimum	1
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life, average	3
Software [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life, average	3
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life, average	5
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life, average	3
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life, minimum	2
Property, plant and equipment, useful life, maximum	12
Software Development [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life, average	2