Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Investments in securities [Abstract]
Investments in securities	$ 29,561	$ 25,845
Securities sold, not yet purchased [Abstract]
Total securities sold, not yet purchased	0	799
Common Stocks [Member]
Investments in securities [Abstract]
Investments in securities	17,687	19,099
Open-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	6,018	6,128
Actively Managed Semi-transparent EFTs [Member]
Investments in securities [Abstract]
Investments in securities	5,320	0
Closed-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	529	618
Other [Member]
Investments in securities [Abstract]
Investments in securities	7	0
Recurring Basis [Member]
Assets [Abstract]
Cash equivalents	152,243	32,661
Investments in securities [Abstract]
Investments in securities	29,561	25,845
Total assets at fair value	181,804	58,506
Securities sold, not yet purchased [Abstract]
Trading - Common Stocks		799
Total securities sold, not yet purchased		799
Recurring Basis [Member] | Common Stocks [Member]
Investments in securities [Abstract]
Investments in securities	17,687	19,099
Recurring Basis [Member] | Open-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	6,018	6,128
Recurring Basis [Member] | Actively Managed Semi-transparent EFTs [Member]
Investments in securities [Abstract]
Investments in securities	5,320
Recurring Basis [Member] | Closed-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	529	618
Recurring Basis [Member] | Other [Member]
Investments in securities [Abstract]
Investments in securities	7
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets [Abstract]
Cash equivalents	152,243	32,661
Investments in securities [Abstract]
Investments in securities	29,561	25,845
Total assets at fair value	181,804	58,506
Securities sold, not yet purchased [Abstract]
Trading - Common Stocks		799
Total securities sold, not yet purchased		799
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Common Stocks [Member]
Investments in securities [Abstract]
Investments in securities	17,687	19,099
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Open-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	6,018	6,128
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Actively Managed Semi-transparent EFTs [Member]
Investments in securities [Abstract]
Investments in securities	5,320
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Closed-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	529	618
Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other [Member]
Investments in securities [Abstract]
Investments in securities	7
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets [Abstract]
Cash equivalents	0	0
Investments in securities [Abstract]
Investments in securities	0	0
Total assets at fair value	0	0
Securities sold, not yet purchased [Abstract]
Trading - Common Stocks		0
Total securities sold, not yet purchased		0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Common Stocks [Member]
Investments in securities [Abstract]
Investments in securities	0	0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Open-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	0	0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Actively Managed Semi-transparent EFTs [Member]
Investments in securities [Abstract]
Investments in securities	0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Closed-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	0	0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other [Member]
Investments in securities [Abstract]
Investments in securities	0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Cash equivalents	0	0
Investments in securities [Abstract]
Investments in securities	0	0
Total assets at fair value	0	0
Securities sold, not yet purchased [Abstract]
Trading - Common Stocks		0
Total securities sold, not yet purchased		0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Common Stocks [Member]
Investments in securities [Abstract]
Investments in securities	0	0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Open-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	0	0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Actively Managed Semi-transparent EFTs [Member]
Investments in securities [Abstract]
Investments in securities	0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Closed-end Funds [Member]
Investments in securities [Abstract]
Investments in securities	0	$ 0
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other [Member]
Investments in securities [Abstract]
Investments in securities	$ 0