GOODWILL AND INTANGIBLE ASSETS (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended		3 Months Ended					12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Kyte	Jun. 30, 2011 Kyte	Dec. 31, 2012 Americas Brokerage	Dec. 31, 2011 Americas Brokerage	Dec. 31, 2010 Americas Brokerage	Dec. 31, 2012 EMEA Brokerage	Dec. 31, 2011 EMEA Brokerage	Dec. 31, 2012 Clearing and Backed Trading	Dec. 31, 2011 Clearing and Backed Trading	Dec. 31, 2012 All other	Dec. 31, 2011 All other	Dec. 31, 2010 All other
Goodwill
Goodwill at the beginning of the period	$ 266,506	$ 268,288			$ 83,289	$ 83,289	$ 83,289	$ 13,851	$ 13,895	$ 40,675	$ 42,413	$ 128,691	$ 128,691	$ 128,691
Adjustments			(945)	(1,546)						(945)	(1,546)
Foreign currency translation	2,416	(236)						546	(44)	1,870	(192)
Goodwill at the end of the period	$ 267,977	$ 266,506			$ 83,289	$ 83,289	$ 83,289	$ 14,397	$ 13,851	$ 41,600	$ 40,675	$ 128,691	$ 128,691	$ 128,691
Additional disclosures
Fair value in excess of carrying value of reporting unit (as a percent)										2.50%