Goodwill and Other Intangible Assets (Details 1) (USD $) In Thousands, unless otherwise specified	9 Months Ended	11 Months Ended
	Aug. 31, 2011	Nov. 30, 2010
Intangible Assets
Gross cost	$ 23,161	$ 4,842
Accumulated amortization	(2,576)	(1,728)
Net carrying amount	20,585	3,114
Weighted average remaining lives (years)		4.2
Exchange and Clearing Organization Membership Interests and Registrations [Member]
Intangible Assets
Gross cost	11,219
Net carrying amount	11,219
Customer Relationships [Member]
Intangible Assets
Gross cost	10,542	4,742
Accumulated amortization	(2,425)	(1,726)
Net carrying amount	8,117	3,016
Weighted average remaining lives (years)	6.8
Trade names (intangible assets) [Member]
Intangible Assets
Gross cost	1,300
Accumulated amortization	(144)
Net carrying amount	1,156
Weighted average remaining lives (years)	1.3
Other Intangible Assets [Member]
Intangible Assets
Gross cost	100	100
Accumulated amortization	(7)	(2)
Net carrying amount	$ 93	$ 98
Weighted average remaining lives (years)	14.0	14.8