SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended							12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Minimum	Dec. 31, 2012 Maximum	Dec. 31, 2012 Kyte	Jul. 02, 2010 Kyte	Dec. 31, 2012 Software revenue Minimum	Dec. 31, 2012 Software revenue Maximum	Dec. 31, 2012 Analytics revenue	Dec. 31, 2012 Market data subscription revenue Minimum	Dec. 31, 2012 Market data subscription revenue Maximum	Dec. 31, 2012 Property, equipment and leasehold improvements Minimum	Dec. 31, 2012 Property, equipment and leasehold improvements Maximum	Dec. 31, 2012 Computer software
Basis of Presentation
Reduction in accounts payable, accrued expenses and rent and occupancy expense	$ 3,215
Reduction in accounts payable, accrued expenses and rent and occupancy expense	335	160	160
Reduction in accounts payable, accrued expenses and rent and occupancy expense related to years prior to 2010	2,560
Significant accounting policies
Number of VIEs consolidated in which Company is the primary beneficiary	1
Allowance for doubtful accounts	1,710	1,453
Useful life													3 years	7 years	3 years
Amortization period of prepaid bonuses and forgivable loans				2 years	4 years
Prepaid bonuses	31,847	36,797
Forgivable employee loans and advances to employees	31,655	23,909
Amortization of prepaid bonuses and forgivable employee loans	26,549	33,652	25,707
Carrying amount of cost-method investments	4,671	4,059
Fair value of available-for-sale securities	3,355	8,263
Period for recognition of deferred revenue								1 year	5 years	3 years	1 year	2 years
Charge to Compensation and Employee Benefits relating to severance costs and restructuring of certain employment agreements		19,443
Net (losses) resulting from remeasurement of foreign currency transactions and balances	$ (3,635)	$ (220)	$ (6,770)
Future commitment to purchase the remaining equity interest (as a percent)						30.00%	30.00%