Fair Value Measurements (Schedule of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value) (Details) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Assets
Securities owned, at fair value	$ 3,400,000	$ 3,991,000
Other equity investment in related party, at fair value	1,036,000
Liabilities
Securities sold, not yet purchased, at fair value	52,000	24,000
Equity Securities [Member]
Assets
Securities owned, at fair value	255,000	922,000
Liabilities
Securities sold, not yet purchased, at fair value	27,000	24,000
UITs [Member]
Liabilities
Securities sold, not yet purchased, at fair value	25,000
Level 1 [Member]
Assets
Securities owned, at fair value	2,977,000	3,455,000
Other equity investment in related party, at fair value
Liabilities
Securities sold, not yet purchased, at fair value
Level 1 [Member] | Equity Securities [Member]
Assets
Securities owned, at fair value	116,000	489,000
Liabilities
Securities sold, not yet purchased, at fair value
Level 1 [Member] | UITs [Member]
Liabilities
Securities sold, not yet purchased, at fair value
Level 2 [Member]
Assets
Securities owned, at fair value	423,000	536,000
Other equity investment in related party, at fair value
Liabilities
Securities sold, not yet purchased, at fair value	52,000	24,000
Level 2 [Member] | Equity Securities [Member]
Assets
Securities owned, at fair value	139,000	433,000
Liabilities
Securities sold, not yet purchased, at fair value	27,000	24,000
Level 2 [Member] | UITs [Member]
Liabilities
Securities sold, not yet purchased, at fair value	25,000
Level 3 [Member]
Assets
Securities owned, at fair value
Other equity investment in related party, at fair value	1,036,000
Liabilities
Securities sold, not yet purchased, at fair value
Level 3 [Member] | Equity Securities [Member]
Assets
Securities owned, at fair value
Liabilities
Securities sold, not yet purchased, at fair value
Level 3 [Member] | UITs [Member]
Liabilities
Securities sold, not yet purchased, at fair value
U.S. government securities [Member]
Assets
Cash and securities segregated for regulatory purposes	97,655,000
Securities owned, at fair value	3,032,000	2,966,000
U.S. government securities [Member] | Level 1 [Member]
Assets
Cash and securities segregated for regulatory purposes	97,655,000
Securities owned, at fair value	2,860,000	2,966,000
U.S. government securities [Member] | Level 2 [Member]
Assets
Cash and securities segregated for regulatory purposes
Securities owned, at fair value	172,000
U.S. government securities [Member] | Level 3 [Member]
Assets
Cash and securities segregated for regulatory purposes
Securities owned, at fair value
Certificates of Deposit [Member]
Assets
Securities owned, at fair value	91,000	91,000
Certificates of Deposit [Member] | Level 1 [Member]
Assets
Securities owned, at fair value
Certificates of Deposit [Member] | Level 2 [Member]
Assets
Securities owned, at fair value	91,000	91,000
Certificates of Deposit [Member] | Level 3 [Member]
Assets
Securities owned, at fair value
Municipal securities [Member]
Assets
Securities owned, at fair value	10,000
Municipal securities [Member] | Level 1 [Member]
Assets
Securities owned, at fair value
Municipal securities [Member] | Level 2 [Member]
Assets
Securities owned, at fair value	10,000
Municipal securities [Member] | Level 3 [Member]
Assets
Securities owned, at fair value
Corporate bonds [Member]
Assets
Securities owned, at fair value	11,000	12,000
Corporate bonds [Member] | Level 1 [Member]
Assets
Securities owned, at fair value
Corporate bonds [Member] | Level 2 [Member]
Assets
Securities owned, at fair value	11,000	12,000
Corporate bonds [Member] | Level 3 [Member]
Assets
Securities owned, at fair value
Options [Member]
Assets
Securities owned, at fair value	1,000
Options [Member] | Level 1 [Member]
Assets
Securities owned, at fair value	1,000
Options [Member] | Level 2 [Member]
Assets
Securities owned, at fair value
Options [Member] | Level 3 [Member]
Assets
Securities owned, at fair value