Receivables and Payables (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Receivables from brokers, dealers and clearing organizations
Broker-dealers	$ 254,031,000	$ 297,916,000
Clearing organizations	23,033,000	12,391,000
Securities borrowed	742,307,000	798,228,000
Allowance for doubtful accounts	(1,029,000)	(1,416,000)
Total	1,018,342,000	1,107,119,000
Payables to brokers, dealers and clearing organizations
Broker-dealers	284,681,000	513,529,000
Clearing organizations	2,798,000	728,000
Securities loaned	737,789,000	823,202,000
Total	1,025,268,000	1,337,459,000
Receivables from customers
Customers	592,139,000	548,287,000
Allowance for doubtful accounts	(1,135,000)	(1,462,000)
Total	591,004,000	546,825,000
Payables to customers
Customers	469,264,000	226,892,000
Total	469,264,000	226,892,000
Allowance for doubtful accounts
Decrease (Increase) in allowance for doubtful debts	(405,000)	1,401,000	203,000
Total write-offs against the allowance	300,000	200,000	100,000
Securities Borrowed and Loaned
Fair value of securities borrowed	710,600,000
Interest earned	17,756,000	19,242,000	19,130,000
Interest incurred	(10,786,000)	(14,589,000)	(14,646,000)
Interest earned (incurred), net	6,970,000	4,653,000	4,484,000
Gain related to adjustments to historical dividend withholdings on securities borrowed	2,500,000
Deposits paid for securities borrowed
Gross Amounts of Recognized Assets	742,307,000	798,228,000
Net Amounts Presented in the Consolidated Statement of Financial Condition	742,307,000	798,228,000
Collateral Received or Pledged (including Cash)	742,083,000	789,317,000
Net Amount	224,000	8,911,000
Deposits received for securities loaned
Gross Amounts of Recognized Liabilities	(737,789,000)	(823,202,000)
Net Amounts Presented in the Consolidated Statement of Financial Condition	(737,789,000)	(823,202,000)
Collateral Received or Pledged (including Cash)	(721,821,000)	(822,382,000)
Net Amount	$ (15,968,000)	$ (820,000)