Receivables and Payables (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Receivables from brokers, dealers and clearing organizations
Broker-dealers	$ 550,607,000		$ 205,975,000
Clearing organizations	37,481,000		2,365,000
Securities borrowed	987,764,000		663,293,000
Allowance for doubtful accounts	(584,000)		(318,000)
Total	1,575,268,000		871,315,000
Payables to brokers, dealers and clearing organizations
Broker-dealers	799,105,000		370,146,000
Clearing organizations	79,793,000		14,945,000
Securities loaned	1,014,515,000		694,682,000
Total	1,893,413,000		1,079,773,000
Receivables from customers
Customers	1,467,028,000		473,852,000
Allowance for doubtful accounts	(1,625,000)		(1,343,000)
Total	1,465,403,000		472,509,000
Payables to customers
Customers	989,646,000		207,738,000
Total	989,646,000		207,738,000
Securities Borrowed and Loaned
Fair value of securities borrowed	951,400,000
Interest earned	5,902,000	3,351,000
Interest incurred	(4,505,000)	(2,417,000)
Interest earned incurred, net	$ 1,397,000	$ 934,000