Receivables and Payables (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Receivables from brokers, dealers and clearing organizations
Broker-dealers	$ 205,975,000	$ 246,560,000
Clearing organizations	2,365,000	413,000
Securities borrowed	663,293,000	618,662,000
Allowance for doubtful accounts	(318,000)	(384,000)
Total	871,315,000	865,251,000
Payables to brokers, dealers and clearing organizations
Broker-dealers	370,146,000	403,432,000
Clearing organizations	14,945,000	108,526,000
Securities loaned	694,682,000	628,000,000
Total	1,079,773,000	1,139,958,000
Receivables from customers
Customers	473,852,000	607,286,000
Allowance for doubtful accounts	(1,343,000)	(1,030,000)
Total	472,509,000	606,256,000
Payables to customers
Customers	207,738,000	272,027,000
Total	207,738,000	272,027,000
Allowance for doubtful accounts
Increase (Decrease) in allowance for doubtful debts	203,000	178,000	(1,689,000)
Total write-offs against the allowance	100,000	100,000	300,000
Securities Borrowed and Loaned
Fair value of securities borrowed	642,700,000
Interest earned	19,130,000	4,994,000
Interest incurred	(14,646,000)	(3,540,000)
Interest earned incurred, net	$ 4,484,000	$ 1,454,000