Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets
Securities owned, at fair value:	$ 656	$ 1,559
Liabilities
Securities sold, not yet purchased, at fair value:	987	1
Recurring basis
Assets
Total Assets	657	1,559
Liabilities
Total Liabilities	987	1
Recurring basis | Money market mutual funds
Assets
Cash and cash equivalents:	1
Recurring basis | Corporate stocks-trading securities
Assets
Securities owned, at fair value:	18	78
Liabilities
Securities sold, not yet purchased, at fair value:	987	1
Recurring basis | Mutual funds
Assets
Securities owned, at fair value:	638	1,481
Recurring basis | Level 1
Assets
Total Assets	657	1,559
Liabilities
Total Liabilities	987	1
Recurring basis | Level 1 | Money market mutual funds
Assets
Cash and cash equivalents:	1
Recurring basis | Level 1 | Corporate stocks-trading securities
Assets
Securities owned, at fair value:	18	78
Liabilities
Securities sold, not yet purchased, at fair value:	987	1
Recurring basis | Level 1 | Mutual funds
Assets
Securities owned, at fair value:	$ 638	$ 1,481