Deposits with Clearing Organizations, Brokers and Banks	9 Months Ended
	Sep. 30, 2021
Deposits with Clearing Organizations, Brokers and Banks [Abstract]
Deposits with Clearing Organizations, Brokers and Banks	Deposits with Clearing Organizations, Brokers and BanksUnder the terms of agreements between the Company and some of its clearing organizations, brokers and banks, balances owed are collateralized by certain of the Company's cash and securities balances. As of September 30, 2021 and December 31, 2020, the Company had a total of $76.8 million and $105.0 million, respectively, in deposit accounts with clearing organizations, brokers and banks that could be used as collateral to offset losses incurred by the clearing organizations, brokers and banks, on behalf of the Company's activities, if such losses were to occur.