Receivable from and Payable to Customers (Notes)	9 Months Ended
Sep. 30, 2017
Receivables and Payable to Customers [Abstract]
Payable to Customers [Text Block]	Receivable From and Payable to Customers As of September 30, 2017, receivable from customers of $45.5 million consists of amounts owed by customers relating to securities transactions not completed on settlement date and receivables arising from the prepayment of a Commission Sharing Agreement (“CSA”), net of an allowance for doubtful accounts. A prepaid CSA is established for research-related disbursements in advance of anticipated customer commission volumes. Such receivables may not be evidenced by contractual obligations. As of September 30, 2017, payable to customers of $202.7 million 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 CIL are fully cross collateralized by client funds, meaning that the Company, for all intents and purposes, has no market risk. Additionally, CIL has no obligation to settle any trade that it deems inappropriate from a risk perspective, adding an important market and counterparty risk mitigating factor.

Receivable From and Payable to Customers

As of September 30, 2017, receivable from customers of $45.5 million consists of amounts owed by customers relating to securities transactions not completed on settlement date and receivables arising from the prepayment of a Commission Sharing Agreement (“CSA”), net of an allowance for doubtful accounts. A prepaid CSA is established for research-related disbursements in advance of anticipated customer commission volumes. Such receivables may not be evidenced by contractual obligations.

As of September 30, 2017, payable to customers of $202.7 million 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 CIL are fully cross collateralized by client funds, meaning that the Company, for all intents and purposes, has no market risk. Additionally, CIL has no obligation to settle any trade that it deems inappropriate from a risk perspective, adding an important market and counterparty risk mitigating factor.