Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets
Securities owned, at fair value:	$ 6,385	$ 5,277
Liabilities
Securities sold, not yet purchased, at fair value:	1,507	438
Recurring basis | Total
Assets
Total Assets	126,719	124,591
Liabilities
Total Liabilities	1,507	441
Recurring basis | Total | Tax free money market mutual funds
Assets
Cash and cash equivalents:	4,532	2,041
Recurring basis | Total | U.S. government money market mutual funds
Assets
Cash and cash equivalents:	113,152	110,901
Recurring basis | Total | Money market mutual funds
Assets
Cash and cash equivalents:	2,645	6,372
Recurring basis | Total | Corporate stocks-trading securities
Assets
Securities owned, at fair value:	1,362	689
Liabilities
Securities sold, not yet purchased, at fair value:	1,507	438
Recurring basis | Total | Mutual funds
Assets
Securities owned, at fair value:	5,023	4,588
Recurring basis | Total | Currency forward contracts
Assets
Other assets	5
Liabilities
Accounts payable and accrued expenses:		3
Recurring basis | Level 1
Assets
Total Assets	126,714	124,591
Liabilities
Total Liabilities	1,507	438
Recurring basis | Level 1 | Tax free money market mutual funds
Assets
Cash and cash equivalents:	4,532	2,041
Recurring basis | Level 1 | U.S. government money market mutual funds
Assets
Cash and cash equivalents:	113,152	110,901
Recurring basis | Level 1 | Money market mutual funds
Assets
Cash and cash equivalents:	2,645	6,372
Recurring basis | Level 1 | Corporate stocks-trading securities
Assets
Securities owned, at fair value:	1,362	689
Liabilities
Securities sold, not yet purchased, at fair value:	1,507	438
Recurring basis | Level 1 | Mutual funds
Assets
Securities owned, at fair value:	5,023	4,588
Recurring basis | Level 2
Assets
Total Assets	5
Liabilities
Total Liabilities		3
Recurring basis | Level 2 | Currency forward contracts
Assets
Other assets	5
Liabilities
Accounts payable and accrued expenses:		$ 3