Fair Value Measurements (Schedule of Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value) (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities sold, not yet purchased, at fair value	$ 88,000
Level 1 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities sold, not yet purchased, at fair value	88,000
Level 2 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities sold, not yet purchased, at fair value
Level 3 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities sold, not yet purchased, at fair value
Equity Securities [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities sold, not yet purchased, at fair value	88,000
Equity Securities [Member] | Level 1 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities sold, not yet purchased, at fair value	88,000
Equity Securities [Member] | Level 2 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities sold, not yet purchased, at fair value
Equity Securities [Member] | Level 3 [Member]
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Securities sold, not yet purchased, at fair value