Receivables and Payables (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Receivables from brokers, dealers and clearing organizations
Broker-dealers	$ 549,743,000		$ 549,743,000		$ 246,560,000
Clearing organizations	11,345,000		11,345,000		413,000
Securities borrowed	513,384,000		513,384,000		618,662,000
Allowance for doubtful accounts	(478,000)		(478,000)		(384,000)
Total	1,073,994,000		1,073,994,000		865,251,000
Payables to brokers, dealers and clearing organizations
Broker-dealers	497,914,000		497,914,000		403,432,000
Clearing organizations	63,761,000		63,761,000		108,526,000
Securities loaned	557,970,000		557,970,000		628,000,000
Total	1,119,645,000		1,119,645,000		1,139,958,000
Receivables from customers
Customers	828,381,000		828,381,000		607,286,000
Allowance for doubtful accounts	(1,247,000)		(1,247,000)		(1,030,000)
Total	827,134,000		827,134,000		606,256,000
Payables to customers
Customers	635,460,000		635,460,000		272,027,000
Total	635,460,000		635,460,000		272,027,000
Securities Borrowed and Loaned
Fair value of securities borrowed	467,700,000		467,700,000
Interest earned	5,114,000	1,372,000	14,794,000	2,699,000
Interest incurred	(4,053,000)	(958,000)	(11,473,000)	(1,802,000)
Interest earned incurred, net	$ 1,061,000	$ 414,000	$ 3,321,000	$ 897,000