Fair Value Measurements (Schedule of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value) (Details) - USD ($)		Jun. 30, 2022	Dec. 31, 2021
Assets
Securities owned, at fair value		$ 3,350,000	$ 3,991,000
Liabilities
Securities sold, not yet purchased, at fair value		9,000	24,000
Equity Securities [Member]
Assets
Securities owned, at fair value		392,000	922,000
Liabilities
Securities sold, not yet purchased, at fair value		9,000	24,000
Level 1 [Member]
Assets
Securities owned, at fair value		3,085,000	3,455,000
Liabilities
Securities sold, not yet purchased, at fair value
Level 1 [Member] | Equity Securities [Member]
Assets
Securities owned, at fair value		240,000	489,000
Liabilities
Securities sold, not yet purchased, at fair value
Level 2 [Member]
Assets
Securities owned, at fair value		265,000	536,000
Liabilities
Securities sold, not yet purchased, at fair value		9,000	24,000
Level 2 [Member] | Equity Securities [Member]
Assets
Securities owned, at fair value		152,000	433,000
Liabilities
Securities sold, not yet purchased, at fair value		9,000	24,000
Level 3 [Member]
Assets
Securities owned, at fair value
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
U.S. government securities [Member]
Assets
Cash and securities segregated for regulatory purposes	[1]	116,818,000
Securities owned, at fair value	[2]	2,845,000	2,966,000
U.S. government securities [Member] | Level 1 [Member]
Assets
Cash and securities segregated for regulatory purposes	[1]	116,818,000
Securities owned, at fair value	[2]	2,845,000	2,966,000
U.S. government securities [Member] | Level 2 [Member]
Assets
Cash and securities segregated for regulatory purposes	[1]
Securities owned, at fair value	[2]
U.S. government securities [Member] | Level 3 [Member]
Assets
Cash and securities segregated for regulatory purposes	[1]
Securities owned, at fair value	[2]
Certificates of Deposit [Member]
Assets
Securities owned, at fair value		92,000	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		92,000	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		$ 0

[1] As of June 30, 2022, the Company had U.S. government securities with market values of approximately $9.8 million, $9.9 million, $62.9 million, $24.3 million and 9.9 million and corresponding maturity dates of May 18, 2023, August 31, 2023, December 31, 2023, January 31, 2024 and May 31, 2024, respectively. As of December 31, 2021, the Company did not have any U.S. government securities classified as cash and securities segregated for regulatory purposes.

[2] As of both June 30, 2022 and December 31, 2021, the U.S. government securities had a maturity date of August 15, 2024.