PROPERTY AND EQUIPMENT (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment
Property and equipment, gross	$ 232,483	$ 176,957
Less: accumulated depreciation and amortization	(143,214)	(112,635)
Property and equipment, net	89,269	64,322
Depreciation	32,818	20,648	16,209
Computer equipment and software
Property, Plant and Equipment
Property and equipment, gross	193,282	146,926
Office equipment, furniture and fixtures and leasehold improvements
Property, Plant and Equipment
Property and equipment, gross	$ 39,201	$ 30,031
Minimum [Member] | Computer equipment and software
Property, Plant and Equipment
Estimated Useful Lives (years)	2 years
Minimum [Member] | Office equipment, furniture and fixtures and leasehold improvements
Property, Plant and Equipment
Estimated Useful Lives (years)	2 years
Maximum [Member] | Computer equipment and software
Property, Plant and Equipment
Estimated Useful Lives (years)	5 years
Maximum [Member] | Office equipment, furniture and fixtures and leasehold improvements
Property, Plant and Equipment
Estimated Useful Lives (years)	11 years