Securities Owned	9 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Securities Owned	Securities OwnedSecurities owned primarily consist of unencumbered U.S. Treasury bills held for liquidity purposes. Total Securities owned were $37.4 million and $58.6 million as of September 30, 2021 and December 31, 2020, respectively. For additional information, see Note 13—“Fair Value of Financial Assets and Liabilities.”