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Concentrations of Credit Risk	12 Months Ended
Concentrations of Credit Risk	Dec. 31, 2018
Risks and Uncertainties [Abstract]
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments could potentially expose us to concentrations of credit risk, including unsecured receivables from the Exchange. A large majority of our revenue and receivables are from the Exchange and its subsidiaries. See also Note 1, "Nature of Operations". Management fee amounts and other reimbursements due from the Exchange and its subsidiaries were $449.9 million and $418.3 million at December 31, 2018 and 2017, respectively.