Receivable from and Payable to Customers	3 Months Ended
	Mar. 31, 2021
Receivables and Payable to Customers [Abstract]
Receivable from and Payables to Customers [Text Block]	Receivable From and Payable To CustomersAs of March 31, 2021 and December 31, 2020, receivable from customers of $199.7 million and $104.0 million, respectively, consist of amounts owed by customers relating to securities transactions not completed on settlement date and receivables arising from prepaid research. As of March 31, 2021 and December 31, 2020, payable to customers of $2.7 billion and $1.7 billion, respectively, include amounts due on cash and margin transactions to the Company's clients, some of which have their assets held by a Company omnibus account, which are included within receivables from brokers, dealers and clearing organizations in the accompanying condensed consolidated statements of financial condition. In the omnibus structure, positions that are owned by Cowen International Ltd are fully cross collateralized by client funds, meaning that the Company, for all intents and purposes, has no market risk. Additionally, Cowen International Ltd has no obligation to settle any trade that it deems inappropriate from a risk perspective, adding an important market and counterparty risk mitigating factor.