Regulatory Authorities (Narrative) (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 ETC [Member] D	Sep. 30, 2012 EGL [Member]	Dec. 31, 2011 EGL [Member]
Regulatory Authorities [Line Items]
Maintenance of net capital of aggregate indebtedness, percent	6.67%
Regulatory net capital, value	$ 100		$ 47,856	$ 67,893
Regulatory net capital exceeding minimum net capital requirement			46,403	66,726
Tier 1 capital		5,000
Minimum liquid assets, amount		3,500
Coverage of operating expenses, days		90
Collateral held in a segregated account at a third-party depository institution		$ 10,000