Concentrations of Credit Risk	12 Months Ended
	Dec. 31, 2020
Risks and Uncertainties [Abstract]
Concentrations of Credit Risk	Concentrations of Credit RiskFinancial instruments that could potentially expose us to concentrations of credit risk include our unsecured receivables from the Exchange. A large majority of our revenue and receivables are from the Exchange and its affiliates. See also Note 1, "Nature of Operations". Net management fee amounts and other reimbursements due from the Exchange and its affiliates were $494.6 million and $468.6 million at December 31, 2020 and 2019, respectively. Given the financial strength of the Exchange and historical experience of no credit losses, we previously did not record a credit loss allowance to these receivables. Upon adoption of ASU 2016-13, we recorded an allowance for current expected credit losses of $0.6 million related to the receivables from the Exchange and affiliates. See also Note 2, "Significant Accounting Policies". There was no material change to this allowance as of December 31, 2020.