Fair Value Measurements (Schedule of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Assets
Segregated securities		$ 1,311,000
Securities owned, at fair value	$ 3,680,000	3,018,000
Liabilities
Securities sold, not yet purchased, at fair value	31,000	116,000	[1]
Equity Securities [Member]
Assets
Securities owned, at fair value	398,000	986,000
Liabilities
Securities sold, not yet purchased, at fair value	31,000	116,000
Unit investment trusts [Member]
Assets
Securities owned, at fair value	1,000
Level 1 [Member]
Assets
Securities owned, at fair value	2,180,000	2,460,000
Liabilities
Securities sold, not yet purchased, at fair value		88,000
Level 1 [Member] | Equity Securities [Member]
Assets
Securities owned, at fair value	139,000	453,000
Liabilities
Securities sold, not yet purchased, at fair value		88,000
Level 1 [Member] | Unit investment trusts [Member]
Assets
Securities owned, at fair value	1,000
Level 2 [Member]
Assets
Securities owned, at fair value	1,500,000	270,000
Liabilities
Securities sold, not yet purchased, at fair value	31,000	28,000
Level 2 [Member] | Equity Securities [Member]
Assets
Securities owned, at fair value	259,000	245,000
Liabilities
Securities sold, not yet purchased, at fair value	31,000	28,000
Level 2 [Member] | Unit investment trusts [Member]
Assets
Securities owned, at fair value
Level 3 [Member]
Assets
Securities owned, at fair value		288,000
Liabilities
Securities sold, not yet purchased, at fair value
Level 3 [Member] | Equity Securities [Member]
Assets
Securities owned, at fair value		288,000
Liabilities
Securities sold, not yet purchased, at fair value
Level 3 [Member] | Unit investment trusts [Member]
Assets
Securities owned, at fair value
Certificates of Deposit [Member]
Assets
Cash and cash equivalents	142,000	142,000
Certificates of Deposit [Member] | Level 1 [Member]
Assets
Cash and cash equivalents
Certificates of Deposit [Member] | Level 2 [Member]
Assets
Cash and cash equivalents	142,000	142,000
Certificates of Deposit [Member] | Level 3 [Member]
Assets
Cash and cash equivalents
U.S. government securities [Member]
Assets
Segregated securities		1,311,000
Securities owned, at fair value	2,040,000	2,007,000
U.S. government securities [Member] | Level 1 [Member]
Assets
Segregated securities		1,311,000
Securities owned, at fair value	2,040,000	2,007,000
U.S. government securities [Member] | Level 2 [Member]
Assets
Segregated securities
Securities owned, at fair value
U.S. government securities [Member] | Level 3 [Member]
Assets
Segregated securities
Securities owned, at fair value
Municipal securities [Member]
Assets
Securities owned, at fair value	938,000
Municipal securities [Member] | Level 1 [Member]
Assets
Securities owned, at fair value
Municipal securities [Member] | Level 2 [Member]
Assets
Securities owned, at fair value	938,000
Municipal securities [Member] | Level 3 [Member]
Assets
Securities owned, at fair value
Corporate bonds [Member]
Assets
Securities owned, at fair value	303,000	25,000
Corporate bonds [Member] | Level 1 [Member]
Assets
Securities owned, at fair value
Corporate bonds [Member] | Level 2 [Member]
Assets
Securities owned, at fair value	303,000	25,000
Corporate bonds [Member] | Level 3 [Member]
Assets
Securities owned, at fair value

[1] Statement of financial condition as of December 31, 2019 represents the pro forma combination of Siebert and StockCross balances. See "Note 3 - Acquisitions" for additional detail.